DL Control Channels [10]

Again this section is mainly taken from [10]. DL control channels convey information essential for system operation. Information on DL control channels is transmitted hierarchically over different time scales from the superframe level to the AAI subframe level. In mixed mode operation (WirelessMAN-OFDMA/Advanced Air Interface), an AMS can access the system without decoding WirelessMAN-OFDMA FCH and MAP messages.

2.8.1 Superframe Header

The Superframe Header (SFH) carries essential system parameters and system configuration information. The SFH is located in the first AAI subframe within a superframe. The SFH uses the last 5 OFDM symbols within the first AAI subframe.

All PRUs in the first AAI subframe of a superframe have 5 OFDM symbols with the 2 stream pilot pattern. The resource mapping process in the SFH AAI subframe is as follows.

The AAI subframe where SFH is located always has one frequency partition F P0. All NP RU

PRUs in the AAI subframe where SFH is located are permuted to generate the distributed LRUs. The permutation and frequency partition of the SFH AAI subframe can be described by DSAC = 0 (all minibands, without subband), DF P C = 0 (reuse 1 only), DCASSB0= 0 (no subband CRU allocated), and DCASM B0 = 0 (no miniband CRU allocated).

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Figure 2.29: Parameters and values for resource allocation of SFH (from [10, Table 806]).

The SFH occupies the first NSF H distributed LRUs in the first AAI subframe of a su-perframe where NSF H ≤ 24. The remaining distributed LRUs in the first AAI subframe of a superframe are used for other control and data transmission. The SFH is divided into two parts: Primary Superframe Header (P-SFH) and Secondary Superframe Header (S-SFH).

Figure 2.29 describes the parameters and values for resource allocation of the SFH.

2.8.2 Primary Superframe Header

The Primary Superframe Header (P-SFH) shall be transmitted in every superframe. The first NP −SF H distributed LRUs of the first AAI subframe are allocated for P-SFH transmission, where N_{P −SF H} is a fixed value.

2.8.3 Secondary Superframe Header

The Secondary Superframe Header (S-SFH) may be transmitted in every superframe. If the S-SFH is present, the S-SFH shall be mapped to the NS−SF H distributed LRUs following the NP −SF Hdistributed LRUs. The value of NS−SF H is indicated in P-SFH IE. The S-SFH can be repeated over two consecutive superframes. The information transmitted in S-SFH is divided into three sub-packets. The sub-packets of S-SFH are transmitted periodically where each sub-packet has a different transmission periodicity as illustrated in Fig. 2.30. The “SP

Figure 2.30: Illustration of periodic transmission of S-SFH SPs with example transmission periodicity of 40 ms, 80 ms and 160 ms for SP1, SP2 and SP3, respectively (Figure 515 in [10]).

scheduling periodicity information” field of S-SFH SP3 is used to indicate the transmission periodicity of the S-SFH SPs (1, 2, 3). Fig. 2.31 shows the transmission periodicity of different S-SFH SPs for different values of “SP scheduling periodicity information” field.

When there is no S-SFH SP in the SFH, the SFH resources are used for transmitting other control information or A-MAP.

2.8.4 Advanced MAP (A-MAP)

The Advanced MAP (A-MAP) carries unicast service control information. Unicast service control information consists of user-specific control information and non-user-specific control information. User-specific control information is further divided into assignment information, HARQ feedback information, and power control information, and they are transmitted in the assignment A-MAP, HARQ feedback A-MAP, and power control A-MAP, respectively.

All the A-MAPs share a region of physical resources called A-MAP region. A-MAP regions shall be present in all DL unicast AAI subframes. When default TTI is used, DL data allocations corresponding to an A-MAP region occupy resources in the AAI subframe where the A-MAP region is located Figure 2.32 illustrates the location of A-MAP region in the

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Figure 2.31: Transmission Periodicity of S-SFH SPs (from [10, Table 807]).

    

()-Figure 2.32: Example of locations of A-MAP regions in a TDD system (From [10, Fig 516]).

TDD mode.

If FFR is used in a DL AAI subframe, both the reuse 1 partition and the power-boosted reuse 3 partition may contain an A-MAP region. In a DL AAI subframe, non-user specific, HARQ feedback, and power control A-MAPs are located in a frequency partition called the primary frequency partition. The primary frequency partition can be either the reuse 1 partition or the power-boosted reuse 3 partition, which is indicated by ABS through S-SFH SP1 IE. Assignment A-MAP can be in the reuse 1 partition or the power-boosted reuse 3 partition or both. The number of assignment A-MAPs in each frequency partition is signaled through non-user specific A-MAP.

The structure of an A-MAP region is illustrated in the example in Figure 2.33. The resource occupied by each A-MAP may vary depending on the system configuration and scheduler operation.

In DL AAI subframes other than the first AAI subframe of a superframe, an A-MAP region consists of the first N_{A−M AP} distributed LRUs in a frequency partition and the LRUs

Figure 2.33: Structure of an A-MAP region (Figure 517 in [10]).

are formed from PRUs with Nsym symbols. In the first DL AAI subframe of a superframe, the A-MAP region consists of the first NA−M AP distributed LRUs after NSF H distributed LRUs occupied by SFH.

2.8.5 Non-user Specific A-MAP

Non-user-specific A-MAP consists of information that is not dedicated to a specific user or a specific group of users. The AMS should firstly decode the non-user-specific A-MAP in the primary frequency partition to obtain the information needed for decoding assignment A-MAPs and HF A-MAPs. The resource occupied by non-user specific information is of fixed size.

2.8.6 HARQ Feedback A-MAP

HARQ feedback A-MAP carries HARQ ACK/NACK information for uplink data transmis-sion.

2.8.7 Power Control A-MAP

Power Control A-MAP carries fast power control command to AMS.

2.8.8 Assignment A-MAP

Assignment A-MAP contains resource assignment information which is categorized into mul-tiple types of assignment A-MAP IEs. Each assignment A-MAP IE is coded separately and carries information for one or a group of AMSs. The minimum logical resource unit in the assignment A-MAP is called MLRU, consisting of NM LRU = 56 data tones.

The assignment A-MAP IE shall be transmitted with one MLRU or multiple concatenated MLRUs in the A-MAP region. The number of logically contiguous MLRUs is determined based on the assignment A-MAP IE size and channel coding rate, where channel coding rate is selected based on AMS link condition.

Assignment A-MAP IEs are grouped together based on channel coding rate. Assignment A-MAP IEs in the same group are transmitted in the same frequency partition with the same channel coding rate. Each assignment A-MAP group contains several logically contiguous MLRUs. The number of assignment A-MAP IEs in each assignment A-MAP group is signaled through non-user specific A-MAP in the same AAI subframe.

If two assignment MAP groups using two channel coding rates are present in an A-MAP region, assignment A-A-MAP group using lower channel coding rate is allocated first, followed by assignment A-MAP group using higher channel coding rate.

If a broadcast assignment A-MAP IE, i.e., the assignment A-MAP IE intended for all the AMSs, exists in a DL AAI subframe, it shall be present at the beginning of either assignment A-MAP group 1 or assignment A-MAP group 3.

All the multicast assignment A-MAP IEs, i.e., all the assignment A-MAP IEs intended for

Figure 2.34: Physical processing block diagram for the P-SFH (Figure 518 in [10]).

a specific group of AMSs, present in any assignment A-MAP group, shall occupy a contiguous set of MLRUs starting from the beginning of the assignment A-MAP group. If the broadcast assignment A-MAP IE is present in the assignment A-MAP group, the multicast assignment A-MAP IEs are located right after the broadcast assignment A-MAP IE. The Group Resource Allocation A-MAP IE is an example of multicast assignment A-MAP IEs.

All the unicast assignment A-MAP IEs intended for a particular AMS shall be transmitted in the same assignment A-MAP group. The DL/UL Basic Assignment A-MAP IEs are an example of unicast assignment A-MAP IEs.

The maximum number of assignment A-MAP IEs in one AAI subframe that the ABS may allocate to an AMS is 8. This number includes all of the assignment A-MAP IEs that are required to be considered by the AMS (its STID, group ID of GRA, Broadcast ID). For a segmentable assignment A-MAP IE (assignment A-MAP IE that occupies more than 1 MLRU in QPSK 1/2, each segment is counted as 1 assignment A-MAP IE.