Chapter 4 Simulation models Setup
4.2 Path reselection model setup
4.2.2 Hop counts
In this section, the multi hop situation is considered. Calculate and take care of the link quality of multi path. AMC comparison that is an important factor is introduced into this path reselection mechanism. The meaning of AMC comparison is to make sure that the throughput can be enhanced after handover with path reselection.
1. SINR Strength with marginal addition :
SINRRS-MS > SINRMRBS-MS + SINRmargin
If the target access station is a RS, a SINR margin must be considered as an additional factor to let MS to stay in the MR-BS’s connection as far as possible.
2. AMC :
1/AMCMRBS-RS + 1/AMCRS-MS < 1/AMCMRBS-MS
The effective throughput is a path reselection concern in this simulation. If the effective throughput of the multi-hop link is not as good as that of the single-hop link, the MR-BS may not consider triggering the MS handover. This constraint is to make sure that the throughput can be enhanced after handover with path reselection. The parameter is referenced to the data payload of P802.16 Rev2/D2. For example, the data payload of QPSK1/2 is 6 bytes, 16QAM1/2 is 12 bytes, and 64QAM1/2 is 18 bytes.
SINR strength comparison is an important factor while MS or BS makes the decision to trigger the handover procedure in 802.16e. In MR system, another key factor that is AMC (Adaptive Modulation and Coding) is introduced into this proposed path reselection mechanism. In the next chapter, the performance impact of each factor introduced into this proposed path reselection will be discussed.
Chapter 5
Simulation Result
In this chapter, the discussion of some parameters that impact the Ping-Pong effect is presented. The simulation result is divided into two sections. The first section introduces what parameters and how to affect the Ping-Pong handover and non Ping-Pong handover. The second section discusses the key factor in the proposed path reselection mechanism of this simulation.
5.1 Analysis of MS handover without path reselection mechanism
In this section, the factors that impact the Ping-Pong effect are discussed first.There are three factors analyzed here, number of relay stations, MS mobility, and number of users.
5.1.1 Ping-Pong effect versus number of relay stations
As the number of relay stations increases, the possibility and frequency of MS handover will increase. For this analysis, three different kind of number of relay stations are discussed, zero RS, three RSs and six RSs. As showed in Figure 5-1, it is obvious that the Ping-Pong effect increases as the numbers of relay stations increases.
The main peak of Ping-Pong handover counts happen in 1000mS (1S). MS handovers to target access station that was the previous access station in 1S, and this case is a serious Ping-Pong effect. Although in the non-RS system, there is a certain number of Ping-Pong handovers that may be the unnecessary handover and the Ping-Pong handovers ratio is 36%. Figure 5-2 shows that the Ping-Pong handovers ratio over the total handover counts. As the numbers of relay stations increases, the frequency of MS handovers increases and the ratio of Ping-Pong handovers decrease. Because of the increasing access station, the MS has higher frequency to handover to another access station that is not the previous access station.
Figure 5-1 Ping-Pong Effect V.S. numbers of relay stations
Figure 5-2 Ping-Pong Handover Counts V.S. numbers of relay stations
5.1.2 Ping-Pong effect versus MS mobility
As the MS mobility decreases, the possibility and frequency of MS handover will decrease. For this analysis, three different kind of Ms mobility are discussed, 50km/h, 25km/h and 10km/h. As showed in Figure 5-3, it is observed that the Ping-Pong effect decreases as the MS mobility decreases and the duration of Ping-Pong handover increases from 1S to 2S. Figure 5-3 and 5-4 show that as the MS mobility decreases, the total handovers and the ratio of Ping-Pong handovers decrease rapidly. When Ms moves slower, it will stay in a more stable environment and have less opportunity to handover to another access station and the duration of handover will also extend.
Figure 5-3 Ping-Pong Effect V.S. MS mobility
Figure 5-4 Ping-Pong Handover Counts V.S. MS mobility
5.1.3 Ping-Pong effect versus number of users
As the users increases, the possibility and frequency of MS handover will increase. For this analysis, three different kind of number of users are discussed, 60 users, 120 users and 180 users. As showed in Figure 5-5, it tells that the Ping-Pong effect increases, as the number of users increases and the main peak of Ping-Pong handover remains 1S. Due to the increasing number of users, the Ping-Pong handover counts increase proportionally. Figure 5-6 also shows that total handover counts and Ping-Pong handover counts increase as number of users increases. Although the Ping-Pong and total handovers increase, the ratio of the Pin-Pong handovers remains the same.
Figure 5-5 Ping-Pong Effect V.S. MS Counts
Figure 5-6 Ping-Pong Handover Counts V.S. MS Counts
5.2 Analysis of MS handover with path reselection mechanism
In this section, all the constraints introduced into the proposed path reselection mechanism are separated to analyze the individual impact on the Ping-Pong Effect reduction. As described in the Chapter 4, two main factors are induced into this path reselection mechanism, SINR and Hop Counts. The detail constraints of these two factors are listed as below.
1. SINR :
z SINR Strength :
SINRTarget > SINRCurrent
z SINR Stability :
Min. SINRTarget > Max. SINRCurrent OR StdDev SINRTarget < StdDev SINRCurrent
2. Hop Counts :
z SINR Strength with marginal addition : SINRRS-MS > SINRMRBS-MS + SINRmargin
z AMC :
1/AMCMRBS-RS + 1/AMCRS-MS < 1/AMCMRBS-MS
5.2.1 Ping-Pong effect versus all constraints
First, all constraints of path reselection are introduced into the simulation to observe the Ping-Pong handovers reduction. The SINRmargin parameter is adjusted to see how this parameter can affect the Ping-Pong Effect. Figure 5-7 and Figure 5-8 show that the Ping-Pong effect is reduced almost 66% at the main peak and 50% of total Ping-Pong handovers. The Ping-Pong handover ratio and total handover counts are almost the same with different SINRmargin so the SINRmargin parameter is not a key factor after this path reselection mechanism uses all constraints to reduce the Ping-Pong Effect.
Figure 5-7 Ping-Pong Effect V.S. All Constraints
Figure 5-8 Ping-Pong Handover Counts V.S. All Constraints
5.2.2 Ping-Pong effect versus only SINR strength marginal addition
Although the result of 5.2.1 shows that the SINRmargin parameter is not a key factor while all constraints are used, it is interesting to analyze the Ping-Pong reduction by using this parameter. Only the constraint, SINRRS-MS > SINRMRBS-MS + SINRmargin, is to reduce the Ping-Pong handover. Figure 5-9 shows that as the SINRmargin parameter increases, the Ping-Pong handover counts decreases. This parameter may not be the most important factor but it really reduces the Ping-Pong effect. If the SINRmargin parameter is large enough, it may be the key factor of this path reselection mechanism. Figure 5-10 shows that if the SINRmargin parameter is not zero, the Ping-Pong handovers and total handover counts can be reduced proportionally as SINRmargin increases.
Figure 5-9 Ping-Pong Effect V.S. Only SINR Marginal Constraints
Figure 5-10 Ping-Pong Handover Counts V.S. Only SINR Marginal Constraints
5.2.3 Ping-Pong effect versus different constraint
In this sector, all constraints are separated to analyze the impact on Ping-Pong effect to find out the most important factor. Four conditions are discussed according to Figure 5-11 and Figure 5-12.
1. Path reselection with only AMC:
1/AMCMRBS-RS + 1/AMCRS-MS < 1/AMCMRBS-MS
The simulation result shows that the AMC constraint is the most important factor for this proposed path reselection mechanism. By this AMC constraint, the main peak of Ping-Pong handovers reduction is 66%, the total Ping-Pong handovers reduction is 51% and the total handovers reduction is 46%. This constraint also decreases the Ping-Pong handover ratio from 33.8% to 30.5%.
2. Path reselection without AMC:
Without AMC constraint, the path reselection mechanism can decrease the Ping-Pong handovers and total handovers because of the other constraints. Other constraints without AMC can also reduce 50% of
Ping-Pong handovers.
3. Path reselection with SINR MinMax Comparison:
Min. SINRTarget > Max. SINRCurrent
This constraint can reduce the main peak of the Ping-Pong handovers but increase a little bit of the total Ping-Pong handovers. It may not be the right individual constraint of path reselection. This constraint should be combined with other constraints.
4. Path reselection with SINR StdDev Comparison:
StdDev SINRTarget < StdDev SINRCurrent
Although this constraint can reduce the Ping-Pong handovers and the total handovers, the impact of reducing the Ping-Pong effect is not so obvious. This constraint is not the key factor as the AMC constraint.
The AMC constraint is the most key factor of all constraint of this proposed path reselection mechanism.
Figure 5-11 Ping-Pong Effect V.S. Different Constraints
Figure 5-12 Ping-Pong Handover Counts V.S. Different Constraints
5.2.4 SINR comparison
In this section, the SINR before handover and SINR improvement after handover are discussed. This discussion is to realize whether the path reselection mechanism can select the right MS to handover or not. Figure 5-13 shows that the path reselection with the AMC constraint and all constraints can select the MS with low enough SINR to start the handover procedure. After Ms handovers to a new access station, MS can gain about 10dB SINR improvement. It is the same as the result by using the path reselection with all constraints. For the handover procedure without this proposed path reselection mechanism, the SINR of MS before handover is higher than other condition. It also gains the lowest SINR improvement of MS after MS finishes the handover procedure. This result indicates that the handover without this path reselection mechanism may select the MS that may not really need to handover to another access station.
Figure 5-13 SINR Comparison of Each Path Reselection Condition
Chapter 6
Conclusion and future work
After the relay station is introduced into the 802.16e system, some issues may happen or enhance. Ping-Pong effect is one of these issues that may cause the ineffective resource usage or increasing system loading. Although one of the purposes of relay station deployment is throughput enhancement, the wrong handover decision may not enhance the throughput. This proposed path reselection can help MR-BS to select the correct MS and make the right handover decision.
The Ping-Pong effect is affected by some factors. In this simulation, three factors, number of relay stations, MS mobility, and number of users, are discussed. The Ping-Pong handovers increase due to the increment of the number of relay stations, MS mobility and number of users. The ratio of the Ping-Pong handovers presents the different result. As the number of relay stations increases, MS has more opportunity to handover to another access station that is not the previous access station. This situation may cause the decrement of the Ping-Pong handovers ratio. If the MS is on a higher speed, it may handover very often due to the unstable environment and this will increase the Ping-Pong handover ratio. For the number of users, the ratio of Ping-Pong handovers remains the same although the total handovers increases as the number of users increases.
There are four factors introduced into the proposed path reselection: SINR strength, SINR stability, SINR Strength with marginal addition, and AMC. According to the simulation result, this proposed path reselection mechanism can reduce almost 66% of the main peak and 50% of total Ping-Pong handovers. After analyzing the performance of each factor, the AMC factor is the most important one. AMC is considered as a throughput concern. This path reselection mechanism using AMC to make sure that the throughput can be enhanced after handover. Not only the link quality (SINR) but also the throughput enhancement are considered to make the handover decision by the MR-BS.
The SINR comparison is the index to analyze the performance of the path reselection mechanism. It is obvious that this proposed path reselection mechanism can choose the MS that really need to handover and also make the MS to handover to the right target access station. The SINR improvement of this mechanism is much
For the next step, some futurer work may be continued. First, study the impact of MS handover using path reselection in non-transparent RS system. Next, find out the difference of system performance and handover procedure of fixed RS system and mobile RS system. Try to implement the path reselection mechanism into the mobile RS system. Finally, study the feasibility to implement this proposed path reselection mechanism into the real RS system.
Reference
[1] IEEE 802.16j, IEEE 802.16’s Mobile Multihop Relay (MMR) Study Group, http://www.ieee802.org/16/sg/mmr/index.html
[2] P802.16Rev2/D2, “Part16: Air interface for Broadband Wireless Access Systems”
December 2007
[3] IEEE P802.16j/D1, “Part16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems” August 2007
[4] H. Nourizadeh, S. Nourizadeh, and R. Tafazoli, “Impact of the inter-relay Handoff on the Relaying System Performance”, IEEE VTC Sept, 2006
[5] Sungho Jeon, Sanghoon Lee, “A Relay-Assisted Handover Technique with Network Coding over Multihop Cellular Networks”, IEEE Communications Letters, Mar. 2007
[6] Ji Hyun Park, Ki-Young Han and Dong-Ho Cho, “Reducing Inter-Cell Handover Events based on Cell ID Information in Multi-hop Relay systems”, IEEE VETECS, April. 2007
[7] Hyunjeong Lee, Sujean Yang, Yanling Lu, IEEE C802.16j-07/084r1, “MS MAC Handover Procedure in an MR Network – Handover Excution”, 2007-01-16
[8] Yong Sun, Dharma Basgeet, Zhong Fan, Paul Strauch, IEEE C802.16j-07_107,
“Handover and its network model for IEEE 802.16j”, 2007-01-08
[9] Gang Shen, Kaibin Zhang, Shan Jin, IEEE C802.16j-07/146, “MS Handover Support in Transparent/ Non-Transparent Relay Mode”, 2007-01-08
[10] Junhong Hui, Kyu Ha Lee, IEEE C802.16j-07/246, “MS handover with transparent RS in centralized multi-hop relay network”, 2007-03-05
[11] David Comstock, John Lee, Zheng Shang, Jingling Zhu, IEEE S802.16j-07/165,
“MS Handover support in Transparent RS”, 2007-01-08
[12] Yukihiro Takatani, Seishi Hanaoka, IEEE C802.16j-07/079, “A new metric for multi-hop path selection”, 2007-01-08
[13] G.Q. Wang, Wen Tong, Peiying Zhu, Hang Zhang, David Steer, IEEE C802.16j-07/213r4, “MR Relay Link (R-link) and Access link monitoring and reporting procedure for Multi-hop path selection”, 2007-04-30
[14] Chie Ming Chou, Wern-Ho Sheen, Fang-Ching Ren, IEEE C802.16j-07/046r2,
“Path selection and reselection for RSs in IEEE 802.16j Multi-hop Relay Network”, 2007-01-16
[15] Shengjie Zhao, Koon Hoo Teo, Jeffrey Z. Tao, Jinyun Zhang, IEEE S802.16j-07/119r1, “Macro Diversity Handover and Fast Access Station Switching for MMR Network”, 2007-01-16
[16] Gamini Senarath, Wen Tong, Peiying zhu, Hang Zhang, David Steer, IEEE 802.16j-06/013r3, “Multi-hop Relay System Evaluation Methodology (Channel Model and Performance Metric), 2007-02-19
[17] I-Kang Fu, Chi-Fang Li, Ting-Chen Song, Wern-Ho Sheen, IEEE S802.16m-07/0606, “Correlation models for Shadow Fading Simulation” 2007-03-13 [18] Sheng-Shih Wang, Hua-Chiang Yin, Shiann-Tsong Sheu, “Symmetric Path Selection in 802.16 Multi-hop Relay Networks with Error Prone Links”, 2008
[19] Sheng-Shih Wang, Hua-Chiang Yin, Yi-Hsueh Tsai, Shiann-Tsong Sheu, “An Effective Path Selection Metric for IEEE 802.16-based Multi-hop Relay Networks”, 2007
[20] Sung-gook Lim, Eunhyun Kwon, Hun-je Yeon, Jaiyong Lee, Mi-Sun Do, Rakesh Taori, “Performance Analysis of Wireless Relaying Networks Using Asymmetric Relay Path”, 2007
[21] Winner, “Final Report on Link Level and System Level Channel Models”, IST-2003-507581 WINNER D5.4 v.1.4, Nov. 18th, 2005
[22] Gudmundson, M., “Correlation model for shadow fading in mobile radio systems”, Electronic Letters, pp.2145-2146, Vol. 27, Issue 23, November 1991.