針對上行頻寬索取與傳輸機制在行動WiMAX系統

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(1)國立交通大學電子工程學系電子研究所碩士班碩士論文. 針對上行頻寬索取與傳輸機制在行動WiMAX系統 Performance Analysis of Uplink Scheduling And Bandwidth Request Mechanism in Mobile WiMAX. 研究生：何玠原指導教授：黃經堯中華民國. 博士. 九十六年十二月.

(2) 針對上行頻寬索取與傳輸機制在行動WiMAX系統之無線資源管理效能分析. Performance Analysis of Uplink Scheduling And Bandwidth Request Mechanism in Mobile WiMAX 研究生：何玠原. Student: Chieh Yuan Ho. 指導教授：黃經堯. Advisor: Ching Yao Huang. 國. 立交. 通. 大. 學. 電子工程學系電子研究所碩士班碩士論文 A Thesis Submitted to Department of Electronics Engineering & Institute of Electronics College of Electrical and Computer Engineering National Chiao Tung University In Partial Fulfillment of the Requirements For the Degree of Master in Electronics Engineering December 2007 HsinChu, Taiwan, Republic of China. 中華民國九十六年十二月.

(3) 針對上行頻寬索取與傳輸機制在行動WiMAX系統之無線資源管理效能分析國立交通大學電子工程學系電子研究所碩士班. 學生: 何玠原. 指導教授:黃經堯博士. 摘. 要. 在這篇論文中，我們介紹了行動 WiMAX 的物理層和媒介接取控制層。而行動 WiMAX 引用了 IEEE 802.16d-2004 和 IEEE 802.16e-2005 兩樣技術標準當參考。我們亦架構了 Mobile WiMAX 系統層級的模擬工具，且實現上行頻寬索取機制。藉此模擬系統，我們完成了一套完整的上行傳輸機制效能分析，並實現了四種最通用的排程演算法。最後，我們更進一步的將不同的排程演算法在單一資料形式與混合資料形式的環境下模擬其效應，以探討不同演算法各自之間在傳輸速率、服務品質控制、以及系統容量等方面的優缺點，並觀察各自最適合的使用時機。這四種排程演算法包含了 Early Deadline First (EDF)、Proportional Fair (PF)、Maximum CINR (MaxCINR)、和 Round-Robin (RR)。另外，我們提出了一套時間延遲限制的概念，可應用於非即時傳輸服務(如 FTP)的排程演算法。這個概念主要是將最小傳輸速度的限制，針對每一個封包，將其轉化為時間上的限制，不但提高了排程器的設計簡便性，也比單純用傳輸速率來當排程的指標的方法，有更好的效能表現。. i.

(4) Performance Analysis of Uplink Scheduling And Bandwidth Request Mechanism in Mobile WiMAX. Student: Chieh-Yuan Ho. Advisor: Ching-Yao Huang. Department of Electronic Engineering Institute of Electronics National Chiao Tung University. Abstract In this thesis, we introduce the PHY and MAC of Mobile WiMAX, which applies the IEEE 802.16d-2004 and IEEE 802.16e-2005 standard as reference. Then, we build up a system-level simulator and a signaling control plane for the uplink bandwidth request Mechanism for the purpose of getting a complete uplink performance analysis and investigating the advantages and disadvantages of different scheduling algorithms, including Early Deadline First (EDF), Proportional Fair (PF), Maximum CINR (MaxCINR), and Round-Robin (RR). We further discuss the capacity and QoS issue in terms of different traffic type in both single traffic and mixed traffic environment. Through the simulation result, the uplink MAC throughput in Mobile WiMAX is clearly revealed, and several common scheduling algorithms are implemented to get a complete uplink performance analysis. In addition, a soft delay bound (SDB) method is used in order to properly schedule non-real-time service. It transforms the minimum rate into time domain delay bound. It facilitates the scheduler design and performs better QoS failure rate than just using data rate as the QoS indicator.. ii.

(5) 致謝. 光陰似箭，碩士班的兩年即將畫下了句點。在這一段過程中，認識許多好夥伴，其中更是有許多在我在專業領域研究上的貴人，很慶幸有你們的陪伴與幫助，在此我願意將我小小的成果分享給在這兩年陪伴我的你們。首先，我要感謝我的指導教授，黃經堯老師，除了在專業上授予我許多關於無線通訊的知識外，也培養我如何去找出問題、分析問題、最後解決問題的能力。也要特別感謝老師在這兩年內，並不反對我往工程以外的領域去發展。兩年來，我參加了許多的創業競賽、並參與一些商業創業相關的活動，老師從沒表示反對過，並支持我去追逐自己的夢想，更常常的提供我一些商業計劃的機會，如IP MALL等，讓我除了電子工程專業之外，有更多機會去磨練培養商業創業的能力。如果沒有黃老師兩年來的支持，我絕對沒有辦法在兩年內完成這麼多的事情，所以在此，我要特別感謝老師兩年來的教誨。另外，要感謝所有實驗室的學長與同學們兩年來的相處與照顧，平常同儕之間的討論，讓我的專業知識能夠快速的累積。最後，要感謝一直很支持我的家人，爸爸、媽媽、弟弟等，不論我做了什麼決定，他們都是全力支持。碩一時，為了不讓自己只鑽研於一個狹小的工程領域，並擴展自己的視野，培養自己的競爭力，我決定修習交大科管輔所，並有計畫的參加一系列的創業競賽與商業個案競賽，之後更產生了創業的熱忱。這一切的決定，都需要爸媽與黃老師的大力支持才能支持我不放棄的繼續做下去。畢竟這將會是一條艱辛、坎坷的路，需要的是不斷的努力與堅持。家人在背後的支持，永遠是我動力的泉源。碩士畢業後，我將繼續攻讀博士，讓自己的專業知識更豐富、更紮實，也希望能在專業上、研究方向、或是其他方面爲Wintech做點貢獻，實驗室越強、越有制度，學生在未來就越能有更好的發展。. iii.

(6) Table of Content Chapter 1 Introduction…………………………………………………1 Chapter 2 Overview of PHY and MAC Layer of Mobile WiMAX 2.1 Introduction to PHY Layer of Mobile WiMAX………………………………….3 2.1.1 OFDMA Basis……………………………………………………………….3 2.1.2 OFDMA Symbol Structure and Sub-Channelization………………………..4 2.1.3 TDD Frame Structure of OFDMA…………………………………………..6 2.1.4 Resource Allocation of Downlink and Uplink Sub-Frame………………….8 2.1.5 Sub-carrier Permutation……………………………………………………..9 2.1.6 Adaptive Modulation and Coding (AMC)…………………………………..12 2.1.7 Hybrid Auto Repeat Request (HARQ)……………………………………....13 2.1.8 Frequency Reuse Factor……………………………………………………..14 2.1.9 Ranging……………………………………………………………………...17 2.1.10 Smart Antenna Technology…………………………………………….…..19 2.2 Introduction to MAC Layer of Mobile WiMAX…………………………………20 2.2.1 Layer Structure………………………………………………………………20 2.2.2 MAC PDU Format…………………………………………………………..23 2.2.3 Fragmentation and Packing …………………………………………………24 2.2.4 QoS based service classes…………………………………………………...25 2.2.5 Network Entry……………………………………………………………….27 2.2.6 Channel condition feedback…………………………………………………28 2.2.7 Handoff………………………………………………………………………28. Chapter 3 Bandwidth Request Mechanism and Scheduling algorithm of Uplink Transmission in Mobile WiMAX 3.1 Bandwidth Request and Grant Mechanism……………………………………32 3.2 Uplink Scheduling Types and QoS services…………………………………...42 3.3 Implementation of Bandwidth Request and Grant Mechanism……………….44 3.4 QoS Parameters Calculation….………………………………………………..48 3.5 Scheduling Algorithms………………………………………………………...50. Chapter 4 Simulation Setup 4.1 19-Cells Wrap-Around Implementation……………………………………….54 4.2 OFDMA Sub-Carriers Parameters Setting…………………………………….56 iv.

(7) 4.3 Link Budget……………………………………………………………………58 4.4 Uplink SINR Computation…………………………………………………….60 4.5 Basic Functions of Radio Resource Management……………………………..61 4.6 Traffic Models…………………………………………………………………63. Chapter 5 Simulation Results 5.1 Throughput Performance…………………………………………………………66 5.1.1 MAC Throughput & AMC Usage for full buffer FTP Users Only………….66 5.1.2 MAC Throughput for FTP Users in mixed-traffic Environment……………71 5.2 Performance of Quality of Service……………………………………………….72 5.2.1 Performance of QoS for full buffer FTP Users Only…..……………………72 5.2.2 Performance of QoS for full buffer VoIP Users Only……………………….76 5.2.3 Performance of QoS in mixed -traffic Environment……...…………………76 5.2.3.1 Performance of QoS for FTP Users in mixed -traffic Environment……77 5.2.3.2 Packet Loss Rate for VoIP Users in mixed -traffic Environment……….80. Chapter 6 Conclusion and Future Work……………………………81 Reference……………………………………………………………….83. v.

(8) Figures and Tables Figure 2-1 Figure 2-2 Figure 2-3 Figure 2-4 Figure 2-5 Figure 2-6 Figure 2-7 Figure 2-8 Figure 2-9 Figure 2-10 Figure 2-11 Figure 2-12 Figure 2-13 Figure 2-14 Figure 2-15 Figure 2-16 Figure 2-17 Figure 2-18 Figure 2-19 Figure 2-20 Figure 2-21 Figure 2-22 Figure 2-23 Figure 2-24 Figure 3-1 Figure 3-2 Figure 3-3 Figure 3-4 Figure 3-5 Figure 3-6 Figure 3-7 Figure 3-8 Figure 4-1 Figure 4-2 Figure 4-3. Basic Architecture of OFDM system………………………………...3 Insertion of Cyclic Prefix (CP)……………………………………….4 OFDMA Sub-Carriers structure……………………………………...4 WiMAX OFDMA Frame Structure…………………….…………….6 DL Resource Allocation……………………………….…………..…9 UL Resource Allocation……………………………….……………..9 Flow chart of OFDMA PUSC mode…………………………………11 Band AMC slot structure……………………………………………..12 frequency reuse (1, 3, 1)……………………………………………...14 frequency reuse (1, 3, 3)……………………………………………...15 frequency reuse (3, 3, 3)……………………………………………...15 fractional frequency reuse inner (1, 3, 1) & outer (1, 3, 3)…………..16 Ranging – frequency and power adjustment…………………………17 Ranging – timing adjustment………………………………………...18 PHY-MAC Structure in Mobile WiMAX…………………………….20 MAC Structure in Mobile WiMAX…………………………………..21 MAC PDU Format…………………………………………………...23 Fragmentation………………………………………………………...24 Packing……………………………………………………………….25 QoS Scheduler………………………………………………………..25 Flow Chart of Network Entry……………………………………...…27 Hard Handoff…………………………………………………………29 Fast Base Station Switching………………………………………….29 Macro Diversity Handover (MDHO)………………………………...31 Request and Grant flow chart………………………………………...33 Unicast Polling……………………………………………………….35 Multicast and broadcast polling……………………………………...37 PM bit usage………………………………………………………….38 MAC PDU with BR Sub-header……………………………………..40 Bandwidth Request MAC Header……………………………………41 UL Service Flow Scheduler…………………………………………..44 Flow Chart of bandwidth request and grant mechanism in VoIP and FTP traffic……………………………………………………………46 Multi-cell Layout and Wrap Around Example……………………….54 the antenna orientations for the system to be used in the wrap-around simulation…………………………………………………………….56 Slot Structure in different OFDMA Zones…………………………...57 vi.

(9) Figure 4-4 Figure 5-1 Figure 5-2 Figure 5-3 Figure 5-4 Figure 5-5 Figure 5-6 Figure 5-7 Figure 5-8 Figure 5-9 Figure 5-10 Figure 5-11 Figure 5-12 Figure 5-13 Figure 5-14 Figure 5-15. Table 2-1 Table 2-2 Table 2-3 Table 2-4 Table 3-1 Table 4-1 Table 4-2 Table 4-3 Table 4-4 Table 4-5 Table 4-6. Uplink SINR computation……………………………………………60 MAC Sector Throughput of uplink transmission with different scheduling algorithms………………………………………………..66 AMC Usage of EDF………………………………………………….69 AMC Usage of RR…………………………………………………...69 AMC Usage of EDF………………………………………………….70 AMC Usage of EDF………………………………………………….70 Throughput Performance of FTP Service in Mixed Traffic (10 VoIP Users)………………………………………………………………...71 Packet Delay Rate of FTP users in uplink transmission……………...72 QoS Failure Rate of FTP users in uplink……………………………..74 Comparison of Packet Delay Rate & QoS Failure Rate……………...74 Performance Comparison of Soft Delay Bound and Average Data Rate…………………………………………..……………………….75 Packet Loss Rate of VoIP service only……………………………….76 Packet Delay Rate of FTP users in mixed Traffic (10 VoIP Users/Cell)……………………………………………………………77 QoS Failure Rate for FTP Service in Mixed Traffic (10 VoIP Users/Cell)……………………………………………………………78 Comparison of FTP QoS Failure Rate in different mixed-traffic…….79 Packet Loss Rate of VoIP service in mixed traffic (10 FTP Users/Cell)……………………………………………………………80 Scalable OFDMA parameters………………………………………...5 Downlink and Uplink sub-carriers setting……………………………5 Supported Code and Modulations……………………………………13 Mobile WiMAX Applications and Quality of Service……………….26 Description of Bandwidth Request Header…………………………..41 DL/UL OFDMA Sub-carriers Setting………………………………..57 Link Budget parameters……………………………………………...58 Path-loss Model Scenarios…………………………………………...59 FTP Traffic Model……………………………………………………63 VoIP Traffic Model…………………………………………………...63 System parameters setting……………………………………………64. vii.

(10) Chapter 1. Introduction. The WiMAX technology, based on the IEEE 802.16-2004 Air Interface Standard is rapidly proving itself as a technology that will play a key role in fixed broadband wireless metropolitan area networks. In December, 2005 the IEEE ratified the 802.16e amendment to the 802.16 standard. This amendment adds the features and attributes to the standard necessary to support mobility. The WiMAX Forum defined system performance and certification profiles based on the IEEE 802.16e-2005 Amendment standard. Going beyond the air interface, the WiMAX Forum defined the end-to-end network architecture for implementing a Mobile WiMAX network as well. Mobile WiMAX is a broadband wireless solution that enables convergence of mobile and fixed broadband networks through a common wide area broadband radio access technology and flexible network architecture. It can achieve extremely high data rate to enable many applications and accommodate subscribers’ demand nowadays. In Mobile WiMAX, Scalable OFDMA (S-OFDMA) technology is used in order to support scalable channel bandwidth from 1.25MHz to 20MHz. And an OFDMA frame is divided into downlink sub-frame and uplink sub-frame in TDD mode. For data traffic, Mobile WiMAX is designed as a connection-based technology, and each connection has a connection ID (CID) and a service flow ID (SFID) for BS to manage the quality of service. In order to ensure QoS quality or perform high system performance, scheduling algorithms, which determine the order of transmission, are highly required in both downlink and uplink to accommodate various demands in different scenarios. In this thesis, we focus on the performance analysis of uplink transmission to address the traffic-load capability in Mobile WiMAX. In our simulation platform, we build the architecture of uplink mechanism by implementing several scheduling. 1.

(11) algorithms and bandwidth request and grant mechanism. The rest of this thesis is organized as follows: In chapter 2, the overview of PHY and MAC layers of Mobile WiMAX are briefly introduced. In chapter 3, Bandwidth Request Mechanism and Scheduling algorithm of Uplink Transmission is discussed in detail. In chapter 4, the setting of simulation platform is addressed. In chapter 5, the simulation results are shown. Finally, the conclusion and future works are given in chapter 6.. 2.

(12) Chapter 2. Overview of PHY and MAC Layer of Mobile WiMAX. 2.1 Introduction to PHY Layer of Mobile WiMAX 2.1.1 OFDMA Basis. a0 (t ). a1 (t ). e−iw0t. e iw0 t. g*(−t). g(t ) e − iw1t. eiw1t. g*(−t). g (t ) h(t ). e−iwnt. eiwnt an (t ). g*(−t). g (t ) Figure 2-1 Basic Architecture of OFDM system. Orthogonal Frequency Division Multiplexing (OFDM) [6,7] is a multiplexing technique that divides the bandwidth into multiple frequency sub-carriers as shown in Figure 2-1. In an OFDMA system, the input data stream is divided into several parallel sub-streams and each sub-stream is modulated and transmitted on a separate orthogonal sub-carrier. The increased symbol duration improves the robustness of OFDM to delay spread. Furthermore, the cyclic prefix (CP) is being introduced in order to completely eliminate Inter-Symbol Interference (ISI) as long as the CP duration is longer than the channel delay spread. The CP is a repetition of the last part of data portion of the block, and it is appended to the beginning of the data payload as shown in Figure 2-2. The function of Cyclic Prefix is to prevent inter-block interference and makes the channel appear circular and permits low-complexity frequency domain equalization. The obvious drawback of Cyclic Prefix is that it. 3.

(13) introduces overhead, which effectively reduces bandwidth efficiency. Since OFDM has a very sharp spectrum, a large fraction of the allocated channel bandwidth can be utilized for data transmission, which helps to reduce the loss in bandwidth efficiency caused by Cyclic Prefix.. Ts. Tg. Tu. Tg. Figure 2-2 Insertion of Cyclic Prefix (CP). 2.1.2 OFDMA Symbol Structure and Sub-Channelization. ... .... ... Figure 2-3 OFDMA Sub-Carriers structure. The OFDMA symbol structure consists of three types of sub-carriers as shown in Figure 2-3: ¾.  Data sub-carriers for data transmission. ¾.  Pilot sub-carriers for estimation and synchronization purposes. ¾.  Null sub-carriers for no transmission; used for guard bands and DC carriers Data and pilot sub-carriers are grouped into subsets of sub-carriers, called 4.

(14) sub-channels. The WiMAX OFDMA PHY [3] supports sub-channelization in both Downlink and Uplink. The minimum frequency-time resource unit of sub-channelization is one slot, which is equal to 48 data tones. Scalable OFDMA The IEEE 802.16e-2005 OFDMA mode is based on the concept of scalable OFDMA supporting various bandwidths to flexibly address the need for various spectrum allocation and application requirements. The scalability is supported by adjusting the FFT size while fixing the sub-carrier frequency spacing at 10.94 kHz. Since the resource unit sub-carrier bandwidth and symbol duration is fixed, the impact to higher layers is minimal when scaling the bandwidth. The Scalable OFDMA parameters are listed in Table 2-1, 2-2. Table 2-1 Scalable OFDMA parameters. Parameters. Values. System Channel Bandwidth (MHz). 1.25. 5. 10. 20. Sampling Frequency (Fp in MHz). 1.4. 5.6. 11.2. 22.4. FFT Size (NFFT). 128. 512. 1024. 2048. 2. 8. 16. 32. Number of Sub-Channels Sub-Carrier Frequency Spacing. 10.94 kHz. Useful Symbol Time(Tb = 1/f). 91.4 microseconds. Guard Time (Tg =Tb/8). 11.4 microseconds. OFDMA Symbol Duration (Ts = Tb + Tg). 11.4 microseconds. OFDMA Symbol Duration (Ts = Tb + Tg). 48. Table 2-2 Downlink and Uplink sub-carriers setting. Parameter. Downlink. Uplink. Downlink. Uplink. System Bandwidth. 5 MHz. 10 MHz. FFT Size. 512. 1024. Null Sub-Carriers. 92. 104. 184. 184. Pilot Sub-Carriers. 60. 136. 120. 280. Data Sub-Carriers. 360. 272. 720. 560. 5.

(15) Sub-Channels. 15. 17. 30. Symbol Period, Ts. 102.9 microseconds. Frame Duration. 5 milliseconds. OFDM Symbols/Frame. 48. Data OFDM Symbols. 44. 35. 2.1.3 TDD Frame Structure of OFDMA. Figure 2-4 WiMAX OFDMA Frame Structure. The PHY Layer in the IEEE 802.16e-2005 standard [3] supports TDD and Full and Half-Duplex FDD operation, but TDD mode is much more common than FDD mode which is usually applied for some specific reasons; TDD mode enables adjustment of the downlink/uplink ratio to efficiently support asymmetric downlink/uplink traffic load. Unlike FDD, which requires a pair of channels, TDD only requires a single channel for both downlink and uplink providing greater flexibility for adaptation to varied global spectrum allocations. In addition, Transceiver designs for TDD mode implementations are less complex and therefore less expensive. Figure 2-4 shows the OFDMA frame structure for Time Division Duplex (TDD) 6.

(16) mode of Mobile WiMAX. Each frame is divided into DL and UL sub-frames separated by Transmit/Receive and Receive/Transmit Transition Gaps (TTG and RTG, respectively) to prevent DL and UL transmission collisions. In the downlink sub-frame, the Preamble is allocated in the beginning in order to execute synchronization which is a critical issue for TDD mode operation. In order to completely address the synchronization issue, system-wide synchronization is highly required. The following introduces control information in the DL/UL sub-frame, which is used to ensure optimal system operation: ¾. Preamble: The preamble, used for synchronization, is the first OFDMA symbol of the frame.. ¾. Frame Control Header (FCH): The FCH follows the preamble. It provides the frame configuration information such as MAP message length and coding scheme and usable sub-channels.. ¾. DL-MAP and UL-MAP: The DL-MAP and UL-MAP provide sub-channel allocation and other control information for the DL and UL sub-frames respectively.. ¾. UL Ranging: The UL ranging sub-channel is allocated for mobile stations (MS) to perform closed-loop time, frequency, and power adjustment as well as bandwidth requests.. ¾. UL CQICH: The UL CQICH channel is allocated for the MS to feedback channel state information.. ¾. UL ACK: The UL ACK is allocated for the MS to feedback DL HARQ acknowledge.. 7.

(17) 2.1.4 Resource Allocation of Downlink and Uplink Sub-Frame The OFDMA slot is a minimum unit for data transmissions. One OFDMA slot occupies one sub-channel and several OFDMA symbols depending on different slot structures. For downlink Full Usage of Sub-carriers (FUSC) using the distributed sub-carrier permutation, one slot is one sub-channel by one OFDMA symbol. For downlink Partial Usage of Sub-carriers (PUSC) using the distributed sub-carrier permutation, one slot is one sub-channel by two OFDMA symbols. For uplink PUSC using either of the distributed sub-carrier permutations, one slot is one sub-channel by three OFDMA symbols. For uplink and downlink Band Adaptive modulation and coding (Band AMC) using the adjacent sub-carrier permutation. One slot is one sub-channel by one, two, three, or six OFDMA symbols. A Data Region is a two-dimensional allocation which contents a group of contiguous sub-channels and OFDMA symbols. All the allocation refers to logical sub-channels. The minimum unit of data mapping is an OFDMA slot. Based on the standard, how many and which resource units would be assigned to a transmission is decided by BS, and the mechanism is different in downlink and uplink transmission. In downlink resource allocation, system will consider the data size and try to fulfill the resource units into sub-channels of frequency domain first. After the frequency domain is fulfilled in that particular user data burst, then it goes to time domain to fulfill resource units until data traffic for that frame is done. In uplink resource allocation, in a particular user data burst, resource units are fulfilled in time domain first, after the time domain resource units are full, then go to the next frequency domain until data traffic in that frame is done. Figure 2-5 and Figure 2-6 show downlink resource allocations and uplink resource allocation mechanism.. 8.

(18) Figure 2-5 DL Resource Allocation. Figure 2-6 UL Resource Allocation. 2.1.5 Sub-carrier Permutation Sub-carrier permutation is a method to assign frequency sub-carriers into sub-channels. The allocation of sub-carriers to sub-channels is accomplished via permutation rule. There are two categories of permutation modes: distributed sub-carrier permutation and adjacent sub-carrier permutation. Distributed permutation means the. 9.

(19) sub-carriers belonging to a sub-channel are selected pseudo-randomly from all sub-carriers. It can significantly reduce interference from other sectors or cells, and avoid fading effect, such as frequency selective fading. The adjacent sub-carrier permutation will form the sub-channel whose sub-carriers coming from adjacent sub-carriers. System using this permutation mode can take advantage of frequency select fading and get multi-user diversity on the frequency domain at the same time. In order to facilitate a wide range of usage and applications under various requirements and geographic constraints, Mobile WiMAX supports different sub-carriers permutation mode for grouping sub-carriers into sub-channels: ¾. Full Usage of Sub-channels (FUSC) This method is used in downlink only and can use all sub-carriers to do permutation for one sub-channel. It can achieve the best frequency diversity by spreading sub-carriers over entire band. It will use distributed permutation mode.. ¾. Partial Usage of Sub-channels (PUSC) This method can be used both in downlink and uplink. It’s the most common permutation method used to implement Mobile WiMAX or 802.16e-2005. Sub-carriers are grouped into several clusters first. And sub-carriers are chosen one by one from each sub-carrier cluster to form a sub-channel. There are two different implementations in Downlink PUSC and Uplink PUSC. The following is the summary of DL-PUSC used 2048 FFT point as an example.. 10.

(20) Subcarrier Clustering. Major Grouping. Cluster Renumbering. Data Tone Cascading. Pilot Tone Extraction. Subcarrier Subchannelization. Figure 2-7 Flow chart of OFDMA PUSC mode. In 802.16e-2005, 2048 carriers include 1681 used tones (data plus pilot tones). Figure 2-7 shows the flow chart of OFDMA PUSC. The first step of DL-PUSC is to divide these 1680 tones into 120 physical clusters of 14 tones. And then Re-number these divided 120 physical clusters with logical indices for the purpose of interleaving the clusters. After that, 2 tones in each of 120 clusters will be taken out as the pilot tones. Then, major grouping is done by dividing 120 clusters into 6 major groups. The even groups have 24 clusters, and the odd ones have 16 clusters. Fourth, all data tones of each of the major groups are concatenated for sub-channel selection. Finally, Data tones are selected from each major group as a sub-channel according to a specific sequence. ¾. Band Adaptive Modulation and Coding (BandAMC) This method also can be applied in downlink and uplink. It is one of the adjacent permutation methods. The total bandwidth is divided into several sub-bands and tries to utilize the frequency select fading to enhance system performance. The following figure shows the basic rule of Band AMC. 11.

(21) sub-carrier allocation.. Figure 2-8 Band AMC slot structure. Take 2048 FFT size as an example, there’re 1729 used tones and 319 guard tones. A band-AMC sub-channel consists of six 9-carrier bins. That is 54 carriers per sub-channel 192 bins in total. And there are four categories of six bins grid according to different OFDMA symbol duration in Band-AMC mode, as shown in Figure 2-8. . 1-OFDMA-symbol duration, 32 sub-channels. . 2-OFDMA-symbol duration, 62 sub-channels.. . 3-OFDMA-symbol duration, 96 sub-channels.. . 6-OFDMA-symbol duration, 192 sub-channels.. 2.1.6 Adaptive Modulation and Coding (AMC) Adaptive modulation and coding (AMC), Hybrid Automatic Repeat Request (HARQ) and Fast Channel Feedback (CQICH) were introduced with Mobile WiMAX to enhance coverage and capacity for WiMAX in mobile applications. Support for QPSK, 16QAM and 64QAM are mandatory in the DL with Mobile WiMAX. In the uplink transmission, 64QAM is optional. Both Convolutional Code (CC) and Convolutional Turbo Code (CTC) with variable code rate and repetition coding are supported. Block Turbo Code and Low Density Parity Check Code (LDPC) are supported as optional features. Table 2-3 summarizes the coding and modulation 12.

(22) schemes supported in the Mobile WiMAX profile the optional UL codes and modulation are shown in italics. Table 2-3. DL. UL. QPSK, 16QAM, 64QAM. QPSK, 16QAM, 64QAM. CC. 1/2, 2/3, 3/4, 5/6. 1/2, 2/3, 5/6. CTC. 1/2, 2/3, 3/4, 5/6. 1/2, 2/3, 5/6. Repetition. x2, x4, x6. x2, x4, x6. Modulation Code Rate. Supported Code and Modulations. 2.1.7 Hybrid Auto Repeat Request (HARQ) Hybrid Auto Repeat Request (HARQ) is also supported by Mobile WiMAX. HARQ is enabled using N channel “Stop and Wait” protocol which provides fast response to packet errors and improves cell edge coverage. Chase Combining and Incremental Redundancy are supported to further improve the reliability of the retransmission. A dedicated ACK channel is also provided in the uplink for HARQ ACK/NACK signaling. Multi-channel HARQ operation is supported. Multi-channel stop-and-wait ARQ with a small number of channels is an efficient, simple protocol that minimizes the memory required for HARQ and stalling [8]. HARQ combined together with CQICH and AMC provides robust link adaptation in mobile environments at vehicular speeds in excess of 120 km/hr.. 13.

(23) 2.1.8 Frequency Reuse Factor Cellular deployment scenarios specify the pattern of radio frequency channel (or carrier) usage in terms of a “frequency reuse factor”. Sub-carriers in the radio frequency band are assigned to different cells or sectors and this allocation is repeated across adjacent sites (cells or sectors) or adjacent cluster of sites throughout the wireless infrastructure. The resulting frequency reuse planning can be indicated as the triplet (c, s, n) where c is the number of BS sites per cluster, s is the number of sectors per BS site and n is the number of unique frequency channels needed for reuse. Typical examples of reuse (1, 3, 1) and (1, 3, 3) are shown in Figure 2-9 and 2-10.. Figure 2-9 frequency reuse (1, 3, 1). 14.

(24) Figure 2-10 frequency reuse (1, 3, 3). ¾. Frequency reuse (3, 3, 3). f1/1 f3/1. f3/2. f3/3. f1/1. f1/2. f1/3 f2/1. f3/1. f3/1. f3/3. f2/2. f2/3. f1/1. f1/3 f2/1. f1/2. f2/2. f2/3. f1/3. f3/2. f3/3. f3/2. f1/2. f2/1. f2/2. f2/3. Figure 2-11 frequency reuse (3, 3, 3). As shown in Figure 2-11, frequency reuse (3, 3, 3) represents for three BS sites per cluster. The total RF channel is divided into three fractions, and each of BS in a cluster operates on a different fraction of the RF channel. Also, there are three unique frequency channels per BS site needed for reuse.. 15.

(25) ¾. Fractional frequency reuse. Figure 2-12 fractional frequency reuse inner (1, 3, 1) & outer (1, 3, 3). In addition to the frequency reuse factors mentioned above, factional frequency reuse can be a more efficient way to reuse the bandwidth without much increasing the interference MSs gets. The sub-channel reuse pattern can be configured so that users close to the base station operate on the zone with all sub-channels available. While for the edge users, each cell or sector operates on the zone with a fraction of all sub-channels available, which is frequency reuse (1, 3, 3), and F1, F2, and F3 represent different sets of sub-channels in the same frequency channel, as shown in Figure 2-12. With this configuration, while fractional frequency reuse is implemented for edge users to assure edge-user QoS quality and throughput the full load frequency reuse (1, 3, 1) is used for center users to fully utilize the air resource and maximize spectral efficiency. Based on network load, the frequency reuse planning can be dynamically adjusted and optimized across sectors or cells and channel interference conditions on a frame by frame basis.. 16.

(26) 2.1.9 Ranging. Figure 2-13 Ranging – frequency and power adjustment. The ranging process in which the MS acquires frequency, time and power adjustments, after which all MS transmissions are aligned with the UL sub-frame received by the BS. Ranging process is based on MS transmitting a signal and BS responding with required adjustments (RNG-REQ/RSP). As shown in Figure 2-13, assume MS #3 is going to enter the ranging procedure. Before ranging, there are a power offset and frequency offset which is unaligned with the uplink sub-frame with the serving BS. Those unaligned offsets in frequency and power domain cause data loss, high packet error rate, high interference, and incapability to decode data burst due to the unsynchronized uplink sub-frame.. 17.

(27) Figure 2-14 Ranging – timing adjustment. In addition to power and frequency adjustment, timing adjustment is also necessary in ranging process. The distances between MSs and the serving BS are R1, R2, and R3 for MS #1, MS #2, and MS #3 respectively. For the purpose of adjusting the timing of MS uplink transmission for the alignment of uplink sub-frame, different transmission timing, T1, T2, and T3 for MS #1, MS #2, and MS #3 respectively are calculated based on the distance between MS and serving BS, so that uplink transmissions of all MSs in a serving BS are synchronized in terms of timing. After frequency, power, and time adjustment as shown in Figure 2-14, the MS is aligned with the serving BS on the uplink sub-frame in terms of those three items, so that the reception of its data burst is able to be done successfully.. 18.

(28) 2.1.10 Smart Antenna Technology Smart antenna technologies typically involve complex vector or matrix operations on signals due to multiple antennas. OFDMA allows smart antenna operations to be performed on sub-carriers. Complex equalizers are not required to compensate for frequency selective fading. OFDMA therefore, is very well-suited to support smart antenna technologies. In fact, MIMO-OFDM/OFDMA is envisioned as the corner-stone for next generation broadband communication systems [11,12]. Mobile WiMAX supports a full range of smart antenna technologies to enhance system performance. The supporting smart antenna technologies include: ¾. Beamforming: With beamforming [13], the system uses multiple-antennas to transmit weighted signals to improve coverage and capacity of the system and reduce outage probability.. ¾. Space-Time Code (STC): Transmit diversity is supported to provide spatial diversity and reduce fade margin.. ¾. Spatial Multiplexing (SM): Spatial multiplexing [16,17] is supported to take advantage of higher peak rates and increased throughput. With spatial multiplexing, multiple streams are transmitted over multiple antennas. If the receiver also has multiple antennas, it can separate the different streams to achieve higher throughput in comparison to single antenna systems. With 2x2 MIMO, SM increases the peak data rate two times by transmitting two data streams. In UL, each user has only one transmit antenna, two users can transmit collaboratively at the same time slot as if two streams are spatially multiplexed from two antennas of the same user. This is called UL collaborative SM.. 19.

(29) 2.2 Introduction to MAC Layer of Mobile WiMAX 2.2.1 Layer Structure. Figure 2-15 PHY-MAC Structure in Mobile WiMAX. As shown in Figure 2-15, MAC Layer includes three sublayers which are Service-Specific Convergence Sublayer (CS), MAC Common Part Sublayer (MAC CPS), and Security Sublayer respectively. And in between each of two sublayers pair, there is a service access point, so-called SAP, as a interface to access the data from the upper layer or downer layer. CS SAP is the interface between MAC layer and Network layer, and PHY SAP is the interface between MAC layer and Physical layer. While the CS and Security sub-layer are in charge of connection management and security management respectively, most of the resource managements are done in the MAC CPS, including PDU generation, handoff, ARQ, network entry, etc. The details about the three sub-layers are introduced in the following.. 20.

(30) Service-Specific Convergence Sublayer Connection Management MAC Common Part Sublayer. Network Entry. PDU Generation. Handoffs. ARQ. PDU Reassembly. BW Management. PHY Burst Scheduling. Power Management (Sleep & Idle Modes). Security Sublayer Privacy & Key Management (PK, EAP, AES, Multicast Security). Figure 2-16 MAC Structure in Mobile WiMAX. In Figure 2-16, the three sub-layers in MAC layer are introduced. ¾. Service-Specific Convergence Sublayer (CS) There are two general service-specific convergence sublayers in 802.16e-2005. that mapping services to and from MAC connections. The ATM convergence sublayer and the packet convergence sublayer are for ATM services and packet-based services such as IP, Ethernet and VLAN respectively. The main purpose of SSCS is to classify service data units (SDUs) into proper MAC connections, preserve or enable QoS, and enable bandwidth allocation. The mapping forms may vary due to the type of service. Furthermore, more complicated functions are also provided by the convergence sublayers such as payload header suppression and reconstruction to enhance air link efficiency. [Eklund02] ¾. MAC Common Part Sublayer (MAC CPS) The 802.16e-2005 MAC Layer supports point-to-multipoint (PMP) architecture. with a central base station (BS) dealing with multiple sectors simultaneously. The MAC Common Part Sublayer is connection-oriented. Each of services is being mapped to one connection even if it is a connectionless service inherently. It enables the service flow to have the capabilities of bandwidth request, QoS 21.

(31) association, data transmission and routing, and all other related actions. Connections are identified by 16-bit connection identifiers (CIDs) and may require continuously granted bandwidth or bandwidth on demand. There is a standard 48-bit MAC address in each MS, but this serves mainly as an equipment identifier, since the primary addresses used during operation are the CIDs. While entering the network, the SS is assigned three management connections per direction. Three different QoS requirements are needed due to these three connections may have different management levels. The first one is the basic connection, which is used for the transfer of short, time-critical MAC and radio link control (RLC) messages. The primary management connection is used to transfer longer, more delay-tolerant messages such as authentication and connection setup. The secondary management connection is used for the transfer of standards-based management messages such as Dynamic Host Configuration Protocol (DHCP), Trivial File Transfer Protocol (TFTP), and Simple Network Management Protocol (SNMP). Except these management connections, transport connections are allocated for the contracted services by MSs. Transport connections are unidirectional for being accommodated to different uplink and downlink QoS and traffic parameters which are usually assigned to services in pairs. There are some additional connections reserved for contention-based initial access, downlink broadcast transmissions, signaling broadcast contention-based polling, and multicast contention-based polling. MSs may be ordered to join multicast polling groups associated with them. [Eklund02] ¾. Security Sublayer Two main protocols work in this security sublayer, one is for encrypting packet. data across the fixed BWA i.e. encapsulation protocol, and the other one is for secure distribution of keying data from BS to MS called Privacy and Key Management 22.

(32) Protocol (PKM). The PKM protocol applies, RSA public-key algorithm, X.509 digital certificates, and strong encryption algorithm to perform secure key exchanges between MSs and BSs. This Privacy protocol is based on the PKM protocol and has been enhanced to fit seamlessly into the 802.16e MAC Layerand to accommodate to stronger cryptographic methods such as AES. 2.2.2 MAC PDU Format. Figure 2-17 MAC PDU Format. The MAC PDU is a data unit between the peer MAC. A MAC PDU consists of a 48bit MAC header, a variable length data payload, and an optional 32 bits Cyclic Redundancy Check (CRC) as shown in Figure 2-17. Sometimes some MAC PDU will not include payload and CRC bits. These kinds of PDUs are used only in the uplink to transmit control message. Those MAC signaling headers include bandwidth request, uplink transmit power report, CINR report, CQICH allocation request, PHY channel report, uplink sleep control, SN report, and feedback functionalities. MAC PDUs also include some subheaders. Those sub-headers are inserted in MAC PDUs following the generic MAC header. Those sub-headers enable the system to perform grant 23.

(33) management, packing, ARQ feedback, and so on. 2.2.3 Fragmentation and Packing MAC SDUs from SSCS will be formatted according to the MAC PDU format in the CPS, possibly with fragmentation and packing due to the precious radio resources and efficient utilization of the resources. In fragmentation process, a SDU is divided into different PDUs payload areas due to the constraint of the MAC PDU size with the maximum 2048 bytes in the IEEE 802.16e standard. In addition, for preventing high Packet error rate due to too large PDU size, dividing SDU properly according to the channel condition is necessary. Figure 2-18 illustrates fragmentation process. In packing process, several SDUs are packed into a single PDU payload for saving the overhead, Generic MAC Header, CRC, and etc. Figure 2-19 illustrates packing process. Both processes may be enabled by either a BS for a downlink connection or a MS for an uplink connection. PHSI. Packet PDU. MAC SDU. Fragmentation MAC SDU. MAC Header. Fragmentation Sub-header. MAC SDU. MAC SDU f1. MAC Header. MAC PDU. Fragmentation Sub-header MAC PDU. Figure 2-18 Fragmentation. 24. MAC SDU f2.

(34) Figure 2-19 Packing. 2.2.4 QoS based service classes. Figure 2-20 QoS Scheduler. In the Mobile WiMAX MAC layer, QoS is provided via service flows as illustrated in Figure 2-20. A service flow of packets is provided with a particular set of QoS parameters. Before identifying a certain type of data service, the base station and user-terminal first establish a logical link between the peer MACs called a connection, and a connection ID (CID) is given to each connections. Each MS can. 25.

(35) have more than one connection. The scheduler of MAC Layer then associates packets traversing the MAC interface into a service flow to be delivered over the connection. Based on scheduling algorithms, the QoS parameters associated with the service flow is the key for the determination of the transmission ordering and scheduling on the air interface. Therefore, the connection-oriented QoS can provide accurate control over the air interface based on their QoS parameters. Since the air interface is usually the bottleneck, the connection-oriented QoS can effectively enable the end-to-end QoS control. The service flow parameters can be dynamically managed through MAC messages to accommodate the dynamic service demand. The service flow based QoS mechanism applies to both DL and UL to provide improved QoS in both directions. Mobile WiMAX supports a wide range of data services and applications with varied QoS requirements as described in Table 2-4. Table 2-4. Mobile WiMAX Applications and Quality of Service. QoS Class. Applications. QoS Specifications. UGS. VoIP. Maximum sustained rate. UnSolicited Grant Service. Maximum latency tolerance Jitter tolerance. rtPS. Streaming Audio, Video. Real-Time Polling Service. Minimum Reserved Rate Maximum Sustained Rate Maximum Latency Tolerance Traffic Priority. ErtPS. Voice with Activity. Minimum Reserved Rate. Extend Real-Time Polling. Detection, Video. Maximum Sustained Rate. Service. Maximum Latency Tolerance Jitter Tolerance Traffic Priority. nrtPS. FTP, HTTP. Minimum Reserved Rate. Non-Real-Time Polling. Maximum Sustained Rate. Service. Traffic Priority. BE. Data Transfer,. Maximum Sustained Rate. Best Effort Service. Web Browsing. Traffic Priority. 26.

(36) 2.2.5 Network Entry. Secured Traffic. Non-Secured Traffic Figure 2-21. Flow Chart of Network Entry. Network entry process is executed while a MS enters the network, or a handoff event occurs. It’s being divided into two main parts which are non-secured traffic and secured traffic. As shown in Figure 2-21, downlink synchronization is executed first to synchronize with downlink sub-frame for acquiring Frame Control Header (FCH) and DL-MAP. While DL-MAP is acquired, the location information of UL-MAP is available in DL-MAP. And uplink parameters are available in UL-MAP. After that, UL-Ranging for time, frequency, and power adjustment is executed through RNG-REQ/RSP message exchanging. Basic capacity negotiation follows with ranging through SBC-REQ/RSP message exchanging. After that, MS authorization and key exchange for security is executed to secure user’s traffic on the air link. Registration to the serving BS is executed while authorization process is complete. The last step of network entry is to establish IP transport connection for the upper layer communication with other networks. 27.

(37) 2.2.6 Channel condition feedback Due to the mobility, channel condition feedback is critical in Mobile WiMAX. The channel condition may change rapidly in moving situation. Therefore, channel condition information of a MS is necessary for determine the suitable modulation and coding scheme to sustain QoS quality and utilize RF resources efficiently. CINR is used as an indicator for channel quality. BS and MS may measure the CINR to get the channel condition information and send it back. In distributed sub-carrier permutation mode, to get downlink channel quality, MS is responsible to measure the preamble or a permutation zone and get CINR value. Then MS shall send REP-RSP message to BS to report the measured CINR. Based on the feedback information, BS can determine the suitable AMC in the next frame. REP-RSP message might be sent in response to REP-REQ message from BS or in an unsolicited fashion. The REP-RSP message could be sent through CQICH. The location of CQICH is different from MSs and is assigned by BS in uplink sub-frame. As to Band-AMC mode, MS will also measure CINR on different band and report the message through CQICH. While the information of uplink channel condition is needed by serving BS, MS might use UL-Sounding Zone to transmit data for BS to execute CINR estimation. 2.2.7 Handoff There are three handoff methods supported within the 802.16e standard – Hard Handoff (HHO), Fast Base Station Switching (FBSS) and Macro Diversity Handover (MDHO). Among these, the HHO is mandatory while FBSS and MDHO are two optional modes. For meeting the QoS requirement of delay-sensitive and high data rate applications, such as video streaming, techniques for optimizing hard handoff within the framework of the 802.16e standard are needed to be developed to achieve the goal of keeping Layer 2 handoff delays to less than 50 milliseconds. The 28.

(38) following is the brief introduction to three different handoff method supported in the 802.16e standard. ¾. Hard Handoff During hard handover the MS communicates with only just one BS in each time. Connection with the old BS is broken before the new connection is established. Handover occurs while the difference between the signal strength measured from neighbor’s cell and the signal strength measured from the current cell is exceeding a certain threshold value for a threshold time duration. As shown in Figure 2-22, in brief, the black thick line at the boarder of the cells presents the place where the hard handover is realized.. Figure 2-22 Hard Handoff. ¾. Fast Base Station Switching (FBSS). Figure 2-23 Fast Base Station Switching 29.

(39) In Fast Base Station Switching (FBSS) shown in Figure 2-23, the MS and BS maintain a list of BSs that are involved with the MS. This set is called a diversity set. Among the BSs in the Diversity set, an Anchor BS is defined, and it plays the role as the serving BS in Hard Handoff. In FBSS, the MS continuously monitors the signal strength of the BSs that are in the diversity set and selects one BS from the set to be the Anchor BS. When operating in FBSS, the MS only communicates with the Anchor BS for uplink and downlink messages including management and traffic connections. Anchor update and diversity set update are two main procedures while operating in FBSS. Compared to Hard Handoff, anchor update procedure performs the significant reduction of HO time which represents the transition time from one Anchor BS to another. It is done by backhaul communication between the current anchor BS and the candidate BS in the diversity set without MSs’ real transmission of explicit HO signaling messages, so the less-than 50 millisecond HO time is acheived. In diversity set update procedure, the MS scans the neighbor BSs and selects those that are suitable to be included in the diversity set in terms of signal strength, Traffic condition, and etc. The MS reports the selected BSs, and the diversity set update procedure is performed by the BS and MS. An important requirement of FBSS is that the data is simultaneously transmitted to all members of a diversity set of BSs that are able to serve the MS.. 30.

(40) ¾. Macro Diversity Handover (MDHO). Figure 2-24 Macro Diversity Handover (MDHO). The basic concept and advantages of Macro Diversity Handover is the same as Soft Handoff mechanism in CDMA2000 or UMTS. From a system-wise point of view, it utilizes more air-link resources from more than one BS to considerably reduce HO time and perform the diversity gain to increase the performance. In Macro Diversity Handover, same as FBSS, a diversity set of BSs and an anchor BS in the diversity set are defined as well. When operating in MDHO, the MS communicates with all BSs in the active set of uplink and downlink unicast messages and traffic meanwhile as shown in Figure 2-24. An anchor BS in the active set not only transmits data traffic, but also takes charge of transmitting control information and DL broadcast message (DL-MAP, UL-MAP, etc) to the MS. For downlink MDHO, two or more BSs provide synchronized transmission of MS downlink data such that diversity combining is performed at the MS. For uplink MDHO, the transmitted data from a MS is received by multiple BSs where selection diversity of the information received is performed. The frame synchronization and same frequency assignment to all members in the diversity set are also the requirement to enable MDHO.. 31.

(41) Chapter 3. Bandwidth Request Mechanism and. Scheduling algorithm of Uplink Transmission in Mobile WiMAX 3.1 Bandwidth Request and Grant Mechanism Request Mechanism Requests refer to the mechanism that MSs use to indicate to the BS that they need UL bandwidth allocation. A Request may come as a BR header or it may come as a PiggyBack Request. The capability of Piggyback Request is optional. Because the UL burst profile can change dynamically, all requests for bandwidth shall be made in terms of the number of bytes needed to carry the MAC PDU excluding PHY overhead. The BR message may be transmitted during any UL allocation, except during any initial ranging interval. BRs may be incremental or aggregate. When the BS receives an incremental BR, it shall add the quantity of bandwidth requested to its current perception of the bandwidth needs of the connection. When the BS receives an aggregate BR, it shall replace its perception of the bandwidth needs of the connection with the quantity of bandwidth requested. The message flow of request and grant is shown in Figure 3-1.. 32.

(42) Figure 3-1 Request and Grant flow chart. 33.

(43) Polling Mechanism Polling is the process by which the BS allocates bandwidth to the MSs specifically for the purpose of making BRs. These allocations may be to individual MSs or to groups of MSs. Allocations to groups of connections and/or MSs actually define BR Contention IEs. The allocations are contained as a series of IEs within the UL-MAP. Note that polling is done on MS basis. Bandwidth is always requested on a CID basis and bandwidth is allocated on an MS basis. Unicast Polling When a MS is polled individually, no explicit message is transmitted to poll the SS. Instead, the MS is allocated, in the UL-MAP, bandwidth which is sufficient to respond with a BR. MSs that have an active UGS connection of sufficient bandwidth shall not be polled individually unless they set the PM bit in the header of a packet on the UGS connection. The message flow of unicast polling is shown in Figure 3-2.. 34.

(44) Figure 3-2 Unicast Polling. 35.

(45) Multicast and Broadcast Polling If insufficient bandwidth is available to individually poll many inactive MSs, some MSs may be polled in multicast groups or a broadcast poll may be issued. Certain CIDs are reserved for multicast groups and for broadcast messages. As with individual polling, the poll is not an explicit message, but bandwidth allocated in the UL-MAP. The difference is that, rather than associating allocated bandwidth with an MS’s Basic CID, the allocation is to a multicast or Broadcast CID. When the poll is a multicast or Broadcast CID, an MS belonging to the polled group may request bandwidth during any request interval allocated to that CID in the UL-MAP by a Request IE. They shall apply the contention resolution algorithm to select the slot in which to transmit the initial BR. The message flow of multicast and broadcast polling is shown in Figure 3-3.. 36.

(46) Figure 3-3 Multicast and broadcast polling. 37.

(47) PM bit MSs with currently active UGS connections may set the PM bit in a MAC packet of the UGS connection to indicate to the BS that they need to be polled to request bandwidth for non-UGS connections. To reduce the bandwidth requirements of individual polling, MSs with active UGS connections need be individually polled only if the PM bit is set. Once the BS detects this request for polling, the process for individual polling is triggered. The procedure is shown in Figure 3-4.. Figure 3-4 PM bit usage. Contention-based focused BRs for WirelessMAN-OFDMA The OFDMA-based PHY specifies a ranging sub-channel and a subset of ranging codes that shall be used for contention-based BRs. The MS needing to request bandwidth shall select, with equal probability, a ranging code from the code subset allocated to BRs. This ranging code shall be modulated onto the ranging sub-channel and transmitted during a Ranging Slot randomly selected from the appropriate ranging. 38.

(48) region in a single frame. Upon detection, the BS shall provide UL allocation for the SS, and the Broadcast CID shall be sent in combination with a CDMA Allocation IE, which specifies the UL region and ranging code that were used by that specific MS. Thus, the selected CDMA code and the broadcast CID allow a MS to determine whether it has been given an allocation by matching these parameters with itself. The MS use the allocation to transmit a BR PDU. If the BS does not issue the UL allocation described above, or the BR MPDU does not result in a subsequent allocation of any bandwidth, the SS shall assume that the ranging code transmission resulted in a collision and follow the contention resolution Contention Resolution Algorithm The mandatory method of contention resolution that shall be supported is based on a truncated binary exponential backoff, with the initial backoff window and the maximum backoff window controlled by the BS. The values are specified as part of the UCD message and represent a power-of-two value. For example, a value of 4 indicates a window between 0 and 15; a value of 10 indicates a window between 0 and 1023. When a MS has information to send and wants to enter the contention resolution process, it sets its internal backoff window equal to the request backoff start defined in the UCD message. The MS shall randomly select a number within its backoff window. This random value indicates the number of contention transmission opportunities that the MS shall defer before transmitting. A MS shall consider only contention transmission opportunities for which this transmission would have been eligible. These are defined by Request IEs in the UL-MAP messages. Note that each IE may consist of multiple contention transmission opportunities. Using BRs as an example, consider that an SS whose initial backoff window is 0 to 39.

(49) 15 and assume it randomly selects the number 11. The SS must defer a total of 11 contention transmission opportunities. If the first available Request IE is for 6 requests, the MS does not use this and has 5 more opportunities to defer. If the next Request IE is for 2 requests, the MS has 3 more to defer. If the third Request IE is for 8 requests, the MS transmits on the fourth opportunity, after deferring for 3 more opportunities. After a contention transmission, the SS waits for a Data Grant Burst Type IE in a subsequent UL-MAP. Once received, the contention resolution is complete. The MS shall consider the contention transmission lost if no data grant has been received in the number of subsequent UL-MAP messages specified by the Contention-Based Reservation Timeout parameter. The MS shall now increase its backoff window by a factor of two, as long as it is less than the maximum backoff window. The SS shall randomly select a number within its new backoff window and repeat the deferring process described above. For BRs, if the MS receives a unicast Request IE or Data Grant Burst Type IE at any time while deferring for this CID, it shall stop the contention resolution process and use the explicit transmission opportunity.. Generic MAC Header. Bandwidth Request Sub-header. Payload. CRC. MAC PDU Figure 3-5 MAC PDU with BR Sub-header. For uplink transmission, the transmission opportunity of a mobile subscriber (MS) is assigned by Serving BS based on the bandwidth request and grant mechanism defined in the IEEE 802.16e-2005 standard. For some certain service flows, such as UGS, rtPS, nrtPS, and ertPS, Bandwidth Request Message is usually done by the 40.

(50) insertion of Bandwidth Request Header (BRH) following Generic MAC Header (GMH), as shown in Figure 3-5. In order to assure the correct reception of Bandwidth Request Message in BS site, the most robust modulation and coding scheme, BPSK+CC 1/2, is applied for BR Messages no matter how good the channel condition is in the present simulation drop. In the simulation platform, VoIP and FTP traffic models are built to represent UGS and nrtPS respectively. For Unsolicited Grant Service (UGS), transmission opportunity is periodically granted in an unsolicited manner to accommodate the QoS quality, while nrtPS only offers unicast polls on a regular basis, which assures that the UL service flow in BS site receives request opportunities even during network congestion. Figure 3-6 and Table 3-1 shows the detail description of Bandwidth Request MAC Header.. Type (3). BR MSB (11). BR LSB (8). CID MSB (8). CID LSB (8). HSC (8). Figure 3-6 Bandwidth Request MAC Header. Table 3-1. Description of Bandwidth Request Header. Name. Size. Description. Type. 3 bits. The type of BR and UL Tx Power Report header. BR. 11 bits. Bandwidth Request: The number of bytes of uplink bandwidth requested by the MS. The bandwidth request is for the CID. The request shall not include any PHY overhead. It is incremental BW request. In case of the Extended rtPS, if the MSB is 1, the. 41.

(51) BS changes its polling size into the size specified in the LSBs of this field.. CID. 8 bits. The CID shall indicate the connection for which uplink bandwidth is requested.. HCS. 8 bits. Header Check Sequence. 3.2 Uplink Scheduling Types and QoS services Uplink QoS Classes ¾. UGS (Unsolicited Grant Service) The UGS is designed to support real-time UL service flows that transport fixed-size data packets on a periodic basis, such as T1/E1 and Voice over IP without silence suppression. The service offers fixed-size grants on a real-time periodic basis, which eliminate the overhead and latency of MS requests and assure that grants are available to meet the flow’s real-time needs. The BS shall provide Data Grant Burst IEs to the MS at periodic intervals based upon the Maximum Sustained Traffic Rate of the service flow. The size of these grants shall be sufficient to hold the fixed-length data associated with the service flow (with associated generic MAC header and Grant management sub-header).. ¾. rtPS (real-time Polling Service) The rtPS is designed to support real-time UL service flows that transport variable-size data packets on a periodic basis, such as moving pictures experts group (MPEG) video. The service offers real-time, periodic, unicast request opportunities, which meet the flow’s real-time needs and allow the SS to specify the size of the desired grant. This service requires more request overhead than UGS, but supports variable grant sizes for optimum data transport efficiency.. ¾. ErtPS (extended real-time Polling Service) Extended rtPS is a scheduling mechanism which builds on the efficiency of 42.

(52) both UGS and rtPS. The BS shall provide unicast grants in an unsolicited manner like in UGS, thus saving the latency of a BR. However, whereas UGS allocations are fixed in size, ertPS allocations are dynamic. The Extended rtPS is designed to support real-time service flows that generate variable-size data packets on a periodic basis, such as Voice over IP service with silence suppression. ¾. nrtPS (non-real-time Polling Service) The nrtPS offers unicast polls on a regular basis, which assures that the UL service flow receives request opportunities even during network congestion. The BS typically polls nrtPS connections on an interval on the order of one second or less. The BS shall provide timely unicast request opportunities. In order for this service to work correctly, the Request/Transmission Policy shall be set properly. The mandatory QoS parameters for this scheduling service are Minimum Reserved Traffic Rate, Maximum Sustained Traffic Rate, Traffic Priority, Uplink Grant Scheduling Type, and Request/Transmission Policy.. ¾. BE (Best Effort Service) The intent of the BE grant scheduling type is to provide efficient service for BE traffic in the UL. In order for this service to work correctly, the Request/Transmission Policy setting shall be set so that the MS is allowed to use contention request opportunities. This results in the MS using contention request opportunities as well as unicast request opportunities and data transmission opportunities.. 43.

(53) 3.3 Implementation of Bandwidth Request and Grant Mechanism. Framework of Uplink Data Transmission. Figure 3-7 UL Service Flow Scheduler. For uplink service flow scheduler, it’s similar to downlink scheduler in aspects of categories of service flows and QoS-based connections. However, while data traffic of mobile subscribers is transmitted by BS site via downlink resource allocation, MSs have to request Serving BS for transmission opportunity in uplink sub-frame via various bandwidth request methods as shown in Figure 3-7, which includes unicast polling service, contention based BR transmission opportunity, non-contention based BR transmission opportunity, unsolicited polling service, and unsolicited grant service. After negotiation with BS site, MS might either acquire desired bandwidth request transmission opportunity for requesting data transmission opportunity in UL sub-frame, or acquire data transmission opportunity in UL sub-frame directly. In this simulation platform, for the simplicity, only unicast polling service, unsolicited polling service, and unsolicited grant service are implemented to. 44.

(54) execute the attempted simulation of only VoIP and FTP traffic. QoS is provided via service flows as illustrated in Figure 3-7. An uplink service flow of packets is provided with a particular set of QoS parameters. Before identifying a certain type of data service, the base station and user-terminal first establish a logical link between the peer MACs called a connection, and a connection ID (CID) is assigned to each connection by MSs. Every MS might have more than one connection. The scheduler of MAC Layer then associates packets traversing the MAC interface into a service flow to be delivered over the connection. Based on scheduling algorithms, the QoS parameters associated with the service flow is the key for the determination of the transmission ordering and scheduling on the air interface. Therefore, the connection-oriented QoS can provide accurate control and maintain good QoS quality over the air interface based on their QoS parameters.. 45.

(55) MSs initially request required bandwidth by sending BR Headers. No. Transmission succeed? Yes BSs grant BRs according to channel condition. No. Yes nrtPS. UGS. Service Flow Yes ?. Reset Periodic Bandwidth Request Counter. Packet lifetime calculation & Channel quality feedback Packet lifetime calculation & Channel quality feedback Periodic Bandwidth Request count - 1. Count > 0. Count = 0 Periodically request required bandwidth by appending BR Header after GMH. Choose a scheduling algorithm and execute Resource Allocation by UL-MAP. System DropCount + 1. System DropCount + 1. UGS No. Data transmission. Periodic Bandwidth Request Count = 0?. Required bandwidth unsolicited grant. nrtPS Yes Yes. Periodic BR transmission succeed?. No. Packet transmission Succeed?. Yes No. Packet Amount = 0?. System DropCount + 1. Yes Read time - 1. Read time = 0?. Yes. Bandwidth Request Header retransmission No System DropCount + 1. Figure 3-8 Flow Chart of bandwidth request and grant mechanism in VoIP and FTP traffic. 46.