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C80216m-08_218r2 ProjectIEEE 802.16 Broadband Wireless Access Working Group http://ieee802.org/16 Title16m Resource Block Indexing Schemes Evaluation Date Submitted 2008-03-10 Source(s)Hujun Yin, Ping Wang Intel Corporation Juejun Liu, Zhigang Rong Huawei Shanpeng Xiao, Wenqi Liao China Mobile Xiaolu Dong, Ying Du CATR Hongyun Qu, Huiying Fang ZTE Shiqiang Suo CATT Jianhua Liu Alcatel Shanghai-Bell Xin Su, Xiaofeng Zhong Tsinghua University E-mail: hujun.yin@intel.comhujun.yin@intel.com zrong@huawei.comzrong@huawei.com xiaoshanpeng@chinamobile.com dongxiaolu@mail.ritt.com.cn qu.hongyun@zte.com.cn suoshiqiang@datangmobile.cn jianhua.liu@alcatel-sbell.com.cn suxin@mail.tsinghua.edu.cn Re:IEEE 802.16m-08/005: Call for Contributions on Project 802.16m System Description Document (SDD). Target topic: Downlink Control Structures. AbstractEvaluation of the different resource block indexing schemes for 16m. PurposeFor discussion Notice This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the participants listed in the Source(s) field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material contained herein. Release The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.16. Patent Policy The contributor is familiar with the IEEE-SA Patent Policy and Procedures: and.http://standards.ieee.org/guides/bylaws/sect6-7.html#6http://standards.ieee.org/guides/opman/sect6.html#6.3 Further information is located at and.http://standards.ieee.org/board/pat/pat-material.htmlhttp://standards.ieee.org/board/pat

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C80216m-08_218r2 2 Motivation Define the methodologies to compare the resource indexing schemes Compare various resource indexing schemes

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C80216m-08_218r2 3 Resource Indexing Metrics Worst case number of bits per-allocation Calculate the worst case number of bits required for an allocation Commonly used metric For worst case design Ignores allocation pattern Ignores the size of allocation Worst case bit cost per-resource block allocated Calculate the worst case bit cost for one RB For worst case design Ignores allocation pattern Takes the size of allocation into consideration Average number of bits per-allocation Calculate the average number of bits required for an allocation assuming a particular allocation pattern For average performance design Take allocation pattern into consideration Ignores the size of allocation Average number of bits per-resource block allocated Calculate the average bit cost to allocate one resource block For average performance design Take allocation pattern into consideration Take the size of allocation into consideration

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C80216m-08_218r2 4 Allocation Pattern Modeling Uniform distribution [RB_min, RB_max] The number of resource block allocated in each allocation is uniformly distributed over 1 RB (RB_min) and the maximum number of RBs (RB_max) Traffic dependent based on EVM traffic model Select packet size distribution based on traffic model in EVM (e.g. AMR 12.2 VoIP traffic model) Fixed MCS @ 1bits/sec/Hz or generate MCS distribution from SLS Calculate resource block allocation distribution from the packet size distribution and MCS distribution

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C80216m-08_218r2 5 Resource Allocation Evaluation Methodologies Method 1: Assume resource blocks are always contiguous in one allocation Calculate the maximum number bits x(n) required of all possible allocations H max Method 2: Assume resource block are always contiguous in one allocation Calculate the worst case bit cost for one RB Method 3: Assume resource block are always contiguous in one allocation Assume allocated resource block size follow distribution P(n) Assume required number of bits to index resource block size n is x(n) Calculate the average number of bits required for one allocation Method 4: Assume resource block are always contiguous in one allocation Assume allocated resource block size follow distribution P(n) Assume required number of bits to index resource block size n is x(n) Calculate the average number of bits required for one RB allocation

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C80216m-08_218r2 6 3GPP LTE Resource Allocation Approaches: Downlink A resource allocation field in each PDCCH includes two parts, a type field and information consisting of the actual resource allocation. PDCCH with type 0 and type 1 resource allocation have the same format and are distinguished from each other via the type field. For system bandwidth less than or equal to 10 PRBs the resource allocation field in each PDCCH contains only information of the actual resource allocation. PDCCH with type 2 resource allocation have a different format from PDCCH with a type 0 or type 1 resource allocation. PDCCH with a type 2 resource allocation do not have a type field. Resource Allocation Type 0 In resource allocations of type 0, a bitmap indicates the resource block groups that are allocated to the scheduled UE. The size of the group is a function of the system bandwidth that is shown: RBG Size System Bandwidth (P) 110 211 - 26 327 - 64 464 - 110 Resource allocation type 0 is charaterized by the following: >> Grouping of RBs (in frequency domain): Group size may depend on system BW >> Bitmap indicates the RB groups to use At most 28 bits for 110 RB system BW At most 13 bits for 25 RB system BW >> Setting the limit on control signaling overhead.

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C80216m-08_218r2 7 3GPP LTE Resource Allocation Approaches: Downlink Resource Allocation Type 1 In resource allocations of type 1, a bitmap indicates to a scheduled UE the resource blocks from the set of resource blocks from one of the P resource block group subsets where P is the resource block group size associated with the system bandwidth that is shown: RBG Size System Bandwidth (P) 110 211 - 26 327 - 64 464 - 110 Resource Allocation Type 1 is characterized by the following: >> In this method, all resource blocks are divided into several sub-groups, wherein one example case dividing into two sub-groups is illustrated. >> The scheduler uses 1 sub-group to allocate resource to one UE. >> With this method, the number of signaling bits can be reduced because the scheduler uses one sub-group which consists of smaller number of RBs. The bitmap size can be expressed N rb /m 2, where m 2 is the number of sub-groups.

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C80216m-08_218r2 8 3GPP LTE Resource Allocation Approaches: Downlink Resource Allocation Type 2 In resource allocations of type 2, the resource allocation information indicates to a scheduled UE a set of contiguously allocated physical or virtual resource blocks depending on the setting of a 1-bit flag carried on the associated PDCCH. PRB allocations vary from a single PRB up to a maximum number of PRBs spanning the system bandwidth. For VRB allocations, the resource allocation information consists of a starting VRB number and a number of consecutive VRBs where each VRB is mapped to multiple non-consecutive PRBs. A type 2 resource allocation field consists of a resource indication value (RIV) corresponding to a starting resource block ( ) and a length in terms of contiguously allocated resource blocks ( ). The resource indication value is defined by: Resource allocation type 2 is characterized by the following: >> In this method, the scheduler allocates resource with the unit of the island which consists of several contiguous RBs. The allocation information indicates the start point and the number of contiguous RBs. >> With this method, the number of signaling bits can be reduced because of compact expression thanks to contiguous RB allocation. However, when the number of islands is large, e.g., more than 2, the number of signaling bits becomes large. Also, it is a drawback that the number of signaling bits varies depending on the number of islands. It impacts on the receiver complexity in the UE. >> The signaling size for this allocation can be expressed, where m3 is the number of islands.

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C80216m-08_218r2 9 Tree Based Allocation Option 1: Radix-2 Binary tree Option 2: Annular tree Option 3: Binary tree/bitmap hybrid

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C80216m-08_218r2 10 Radix-2 Binary Tree Bit overhead - Number of base nodes: N; - Number of Radix-2 based Nodes: - Number of Total Nodes based on the radix-2 tree: - Bit Overhead: ceil(log2(L)) Bit Overhead of Radix-2-based Tree in case of N = 16. RBs Allocated 12345678910111213141516 Granularity Supported 12X4XXX8XXXXXXX16 Bit Overhead x(n) [Bits] 552x55 3x552x5 3x52x53x5 4x55

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C80216m-08_218r2 11 Annular Tree Annular Channel Tree Structure >> The base nodes are located on the outmost circle. The channel tree maintains a triangular structure for the outmost three levels and then switches to a power of two structure for the remaining levels. Such a structure results in a balance between the overhead associated with making time-frequency resource assignments and flexibility in the assignments. The levels of annular channel tree can be extended with the number of base nodes increasing. For the systems supporting the number of base nodes in the range of 2^n and 2^(n-1), n>2, the structures of annular channel tree are similar, except the number of null base nodes( null base node does not map to physical time-frequency resources). >> Bit overhead - Number of base nodes: N; - Number of Radix-2 based Nodes: - Number of Total Nodes based on the annular tree: - Bit Overhead ceil(log 2 (L)) Number of Nodes (N = 16) Levels of Nodes [ceil(log2(N))] Number of Continuous or Spaced Resource Blocks to Be Allocated [for example, N = 16] 2 ceil(log2(N)) = 1611 22 33 2 ceil(log2(N))-1 = 844 2 ceil(log2(N))-2 = 456 2 ceil(log2(N))-3 = 2610 2 ceil(log2(N))-4 = 1716

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C80216m-08_218r2 12 Annular Tree Structure >> Take example - Number of base nodes: N = 32; - Number of Radix-2 based Nodes: M=2 5 = 32; - Number of Total Nodes based on the annular tree: L = 4M-1 = 4*32-1=127; - Bit Overhead for Option 1:log 2 (L) = log 2 (127) = 7bits

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C80216m-08_218r2 13 Annular Tree Indexing Number of Nodes (N) Levels of Nodes [ceil(log 2 (N))] Granularity of Continuous or Spaced Resource Blocks to Be Allocated Relationships 2 ceil(log2(N)) 11G0G0 22G1G1 33G2G2 2 ceil(log2(N))-1 44G3G3 2 ceil(log2(N))-2 56G 4 = G 3 +2 2 ceil(log2(N))-3 610G 5 = G 4 +4 …… 1L = ceil(log 2 (N))+3 NG L =G L-1 +2 (L-4) (L>=4) Granularity of Continuous or Spaced Resource Blocks to be Allocated for Annular Channel Tree Structure

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C80216m-08_218r2 14 Annular Tree Indexing (cont d) Granularity of Continuous or Spaced Resource Blocks to be Allocated for Annular Channel Tree Structure is illustrated in case of N = 16.

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C80216m-08_218r2 15 Annular Tree Average Overhead RBs Allocated 12345678910111213141516 Granularity upported 1234X6XXX10XXXXX16 Bit Overhead [Bits] 66662x66 6 3x66 Average Bit Overhead of Continuous or Spaced Resource Blocks to be Allocated for Annular Channel Tree Structure is illustrated in case of N = 16.

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C80216m-08_218r2 16 Tree/Bitmap Hybrid Hybrid of a Power of Two Channel Tree and Bitmap Based Assignments >> The parent node is signaled using the power of two channel tree, while the child nodes are signaled using a bitmap, where each bit corresponds to one channel tree node. The delineation between the power of two signaling and the bitmap signaling is a system parameter, thereby making the assignment overhead flexible. >> Take example that the number of base nodes is 16 for allocations with bitmap indication. - Example 1: Parent Node 6 + bitmap 1000 = base node 27 - Example 2: Parent Node 4 + bitmap 1110 = base nodes 19, 20, 21 - Example 3: Parent Node 0 + bitmap 1100 = channel tree nodes 3, 4 >> Bit Overhead [Which level of the child nodes is the bitmap indicated in relation to the parent nodes?] - Number of Base Nodes: N; - Number of Radix-2 Nodes: M = 2 ceil(log2(N)) ; - System parameter delineating between the power of two signaling and bitmap signaling: ; - Bit Overhead for Option 2:

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C80216m-08_218r2 17 Tree/Bitmap Hybrid Indexing Granularity of Continuous or Spaced Resource Blocks to be Allocated for Hybrid of a Power of Two Channel Tree and Bitmap Based Assignments [in case of N = 16] Number of Nodes [ceil(log 2 (N))-log 2 (D_Lin) - K] Bitmap Size [log 2 (D_Lin) =2] Levels of Parent Nodes [K] Granularity of Resource Blocks Relationships 4log 2 (D_Lin)01,2,3,4G0G0 2log 2 (D_Lin)12,4,6,8G 1 = 2 K *G 0 1log 2 (D_Lin)24,8,12,16G 2 = 2*G 1 = 2 K *G 0 Note: The granularity depends on the number of bits for the bitmap (D_Lin). In the above example, the granularity of resource blocks to be allocated is 1,2,3,4,6,8,12, and 16.

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C80216m-08_218r2 18 Tree/Bitmap Hybrid Indexing (cont d) Granularity of Continuous or Spaced Resource Blocks to be Allocated for Hybrid of a Power of Two Channel Tree and Bitmap Based Assignments is illustrated [N = 16].

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C80216m-08_218r2 19 Tree/Bitmap Hybrid Average Overhead Average Bit Overhead of Continuous or Spaced Resource Blocks to be Allocated for Hybrid of a Power of Two Channel Tree and Bitmap Based Assignments is illustrated in case of N = 16. RBs Allocated12345678910111213141516 Granularity Supported1234X6X8X10X12XXX16 Overhead for Bitmap4 bits Overhead for Parent Nodes3 bits Bit Overhead [bits]77772x77 7 7 7 7

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C80216m-08_218r2 20 Uniformly Distributed Resource Allocation Uniformly distributed resource allocation within [RB_min, RB_max] Contiguous resource block for each allocation Number of resource blocks=128 ApproachesAnnular Channel Tree Hybrid Channel Tree LTE Resource AllocationRadix-2- Based Tree Bitmap: 4bits Bitmap: 8 bits Type 0*Type 1*Type 2 Bit Overheadceil(log 2 ( 4*128-1)) = 9 bits 4+6 = 10 bits 8+5 = 13 bits 32 bits ceil(log 2 (12 8*(128+1))) = 14 bits ceil(log 2 (2*12 8-1)) = 8 bits Worst case overhead per allocation 45 bits40 bits39 bits32 bits 14 bits48 bits Worst case bit cost per RB 91013832148 Average overhead per allocation 27 bits26 bits 32 bits 14 bits28 bits Average bit cost per RB0.72960.73140.78401.01464.05850.59430.7621 Note: assume that the number of nodes is 128, which is corresponding to 20MHz bandwidth. *Note that LTE resource allocation type 0 and typ1 is not suitable for small packet size (e.g. VoIP) traffic due to the fact that the granularity of allocation for type 0 is 4RBs and that the granularity of allocation for type 1 is 1RB in case of the 20MHz (N = 128).

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C80216m-08_218r2 21 VoIP with MCS Distribution VoIP packet size: 44bytes (AMR 12.2) Resource block size: 12x6 Number of resource blocks: 128 MCS distribution generated from WiMAX SLS Contiguous resource allocation

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C80216m-08_218r2 22 IndexMCSSEPMF 3QPSK (1/2) Rep 20.50.318 4QPSK (1/2) STBC10.209 5QPSK (3/4) STBC1.50.058 616 QAM(1/2) STBC20.207 716 QAM(3/4) STBC30.037 864 QAM(1/2) STBC30.089 964 QAM(2/3) STBC40.031 1064 QAM(3/4) STBC4.50.024 1164 QAM(5/6) STBC50.016 12QPSK(1/2) SM20.001 13QPSK (3/4) SM30.000 1416QAM(1/2) SM40.000 1516QAM(3/4) SM60.007 1664QAM(1/2) SM60.004 1764QAM(2/3) SM80.000 1864QAM(3/4) SM90.000 1964QAM(5/6) SM100.000 MCS Distribution Sample MCS distribution from WiMAX SLS with mixed mobility (60% PB3, 30% VA30, 10% VA 120)

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C80216m-08_218r2 23 Overhead for VoIP Allocations Worst case bit overhead per allocation Worst case bit cost per RB Average bit overhead per allocation Average bit cost per RB Annular Tree18 bits4.512 bits2.5221 Hybrid Tree (Bitmap: 4bits) 20 bits514 bits2.8024 Hybrid Tree (Bitmap: 8bits) 26 bits6.518 bits3.6431 LTE Resour ce Allocati on Type 0*32 bits4 2.0107 Type 1*32 bits1632 bits8.0428 Type 214 bits7 3.5187 Radix-2 Based Tree 16 bits5.3314 bits3.0728 *Note that LTE resource allocation type 0 and typ1 is not suitable for small packet size (e.g. VoIP) traffic due to the fact that the granularity of allocation is 4RBs and that the granularity of allocation for type 1 is 1RB in case of the 20MHz (N = 128).

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C80216m-08_218r2 24 Conclusions Worst case bit cost per allocation is not a good design criterion –Average bit cost per allocation provides better measure of bit overhead for realistic traffic patterns –Average/worst case bit cost per RB provides better measure of normalize bit overhead for each RB allocated Uniformly distributed allocation pattern is not a good pattern to evaluate the resource indexing overhead –More realistic traffic model should be used –Traffic model that is sensitive to resource indexing overhead (e.g. VoIP) should be used –More accurate MCS level distribution model should provide better resource indexing overhead calculation

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