1. Thomas Eriksson Tony Ottosson Arne Svensson Chalmers University of Technology Sweden Methods for Compression of Feedback in Adaptive Multi-carrier 4G Schemes Víctor P. Gil Jiménez Ana García Armada M. Julia Fernández-Getino García University Calos III de Madrid Spain

2. COST 289 Final Workshop. Göteborg 2007 Outline OFDMA for Downlink in 4G.OFDMA for Downlink in 4G. Feedback information.Feedback information. Opportunistic Feedback.Opportunistic Feedback. System Description.System Description. Algorithms for compression:Algorithms for compression: –Time correlation –Frequency correlation –Time-Frequency correlation Results.Results. Conclusions.Conclusions.

3. COST 289 Final Workshop. Göteborg 2007 OFDMA for downlink in 4G Several techniques for Downlink.Several techniques for Downlink. OFDMA (Orthogonal Frequency Division Multiple Access) is one of the candidates.OFDMA (Orthogonal Frequency Division Multiple Access) is one of the candidates. The BS (Base Station) allocates the different user’s transmission across the orthogonal frequencies.The BS (Base Station) allocates the different user’s transmission across the orthogonal frequencies. Time Frequency

4. COST 289 Final Workshop. Göteborg 2007 Feedback Information The Adaptive Modulation selects the adequate Modulation and Coding Scheme (MCS) according to instantaneous channel conditions for each terminal.The Adaptive Modulation selects the adequate Modulation and Coding Scheme (MCS) according to instantaneous channel conditions for each terminal. Channel is usually known (estimated/predicted) at the receiver.Channel is usually known (estimated/predicted) at the receiver. The receiver should feedback this information.The receiver should feedback this information. It may be highly rate-demanding.It may be highly rate-demanding. Reduction & Compression

5. COST 289 Final Workshop. Göteborg 2007 Opportunistic Feedback The scheduler usually selects the best user(s) for transmitting. Maximum Throughput criterion.The scheduler usually selects the best user(s) for transmitting. Maximum Throughput criterion. It is a waste of resources if a terminal with a bad channel feeds back its data (it will never be served except for fairness policies).It is a waste of resources if a terminal with a bad channel feeds back its data (it will never be served except for fairness policies). The BS broadcasts a minimum quality for feeding back.The BS broadcasts a minimum quality for feeding back.

6. COST 289 Final Workshop. Göteborg 2007 Opportunistic Feedback Some Results UMTS Vehicular A Channel Prob of finding a sub-carrier able to tx >= 4 bits (Load factor = % subcarr occupied when user arrives)

7. COST 289 Final Workshop. Göteborg 2007 Opportunistic Feedback Some Results Load Factor = 0 %

8. COST 289 Final Workshop. Göteborg 2007 System Description Adapt. P/S AdaptiveDemod. DataS/P Adap. Mod. IFFT P/S CP Feedback Decode/Expand FFT S/P CP Feedback Encode/Compress Ch. Est. Base StationTerminal Data

9. COST 289 Final Workshop. Göteborg 2007 System Description Parameters Downlink OFDMA.Downlink OFDMA. 512 sub-carriers (416 useful for data).512 sub-carriers (416 useful for data). Sub-carriers divided into groups of 8 sub-carriers during 12 OFDM symbols = a chunk.Sub-carriers divided into groups of 8 sub-carriers during 12 OFDM symbols = a chunk. 52 chunks in total.52 chunks in total. The same MCS in the same chunk but different (possibly) among them. Adaptive Modulation at chunk level.The same MCS in the same chunk but different (possibly) among them. Adaptive Modulation at chunk level. Available modulations: BPSK – 256 QAM.Available modulations: BPSK – 256 QAM. UMTS channel models: vehicular A, pedestrian A.UMTS channel models: vehicular A, pedestrian A.

10. COST 289 Final Workshop. Göteborg 2007 System Description A Chunk

11. COST 289 Final Workshop. Göteborg 2007 Algorithms for compression Huffman coding for compression. Needs well conditioned data.Huffman coding for compression. Needs well conditioned data. Using Time correlation.Using Time correlation. Using Frequency correlation.Using Frequency correlation. Using Time-Frequency correlation.Using Time-Frequency correlation. (BPSK, QPSK, … 64QAM)

12. COST 289 Final Workshop. Göteborg 2007 Algorithms for Compression Time and Frequency Correlation Frequency Time Feed-back difference between actual and former chunk

13. COST 289 Final Workshop. Göteborg 2007 Algorithms for Compression Iterative Time - Frequency Huffman code 0 Huffman code 1 Huffman code 63 … 1 1 2 88 1... Time Frequency 1 1 ?P1 P2 P7 P8 … Design a Huffman code for each combination b i t-1, b i-1 t : 64 codes

14. COST 289 Final Workshop. Göteborg 2007 1 Algorithms for Compression Block Time - Frequency Time Frequency Huffman code 0 Huffman code 1 Huffman code 511 … 1 1 1 88 1... 1 2 8 1?P1 P2 P7 P8 … 1 Design a Huffman code for each combination b i-1 t-1, b i t-1, b i+1 t-1 : 512 codes

15. COST 289 Final Workshop. Göteborg 2007 Results Comparison to other algorithms 30 users. UMTS Vehicular A channel. 50 km/h and SNR = 20 dB30 users. UMTS Vehicular A channel. 50 km/h and SNR = 20 dB

16. COST 289 Final Workshop. Göteborg 2007 Results UMTS Vehicular A Channel 30 users30 users

17. COST 289 Final Workshop. Göteborg 2007 Results UMTS Pedestrian A Channel 30 users30 users

18. COST 289 Final Workshop. Göteborg 2007 Results Robustness 100 km/h. AWGN Feedback Channel. Different Refresh Rate100 km/h. AWGN Feedback Channel. Different Refresh Rate

19. COST 289 Final Workshop. Göteborg 2007 Conclusions Opportunistic feedback allows 50 % of reduction in feedback data.Opportunistic feedback allows 50 % of reduction in feedback data. The compression of feedback data by using time, frequency or both correlation is feasible and offers compression in the range of 50 % more.The compression of feedback data by using time, frequency or both correlation is feasible and offers compression in the range of 50 % more. Time-Frequency techniques exhibit better performance than the others (in general).Time-Frequency techniques exhibit better performance than the others (in general). Compression algorithms jointly with Opportunistic feedback allow reductions of more than six times.Compression algorithms jointly with Opportunistic feedback allow reductions of more than six times. Once the codes are designed and stored, complexity is almost negligible.Once the codes are designed and stored, complexity is almost negligible. Time – Frequency algorithms need refresh for robustness.Time – Frequency algorithms need refresh for robustness. Future OFDMA systems are closer to be implemented.Future OFDMA systems are closer to be implemented.

20. COST 289 Final Workshop. Göteborg 2007 Thank you very much