GCM Communications Technology September 2001 Building the Global Link Over 90Mbps IEEE 802.11 applications using GCM Vicente Díaz and Daniel Hernanz GCM Communications Technology Divino Vallés 2, 2-F 28805 Alcalá de Henares Madrid (Spain) +34 918883813, vdiaz@gcmcom.com V. Diaz, GCMcom Technology

Outline Introduction to GCM. Main characteristics. Why using GCM? September 2001 Outline Introduction to GCM. Golay sequences properties. How it works. Main characteristics. Aspects to certification. Processing gain and jamming properties. Preambles and throughput. Hardware complexity. Scalability and complexity. Why using GCM? Advantages. Summary. V. Diaz, GCMcom Technology

September 2001 Golay Code Modulation Uses binary Golay complementary sequences to encode symbols. For 11 Mbps: One pair of sequences. Length 16 (higher PG than 11 bits barker). Same bandwidth (QASK modulation spectrum). For 22 Mbps: Two pairs of fully orthogonal 16 bits sequences. V. Diaz, GCMcom Technology

September 2001 Golay sequences A pair of, length N, Golay sequences (A,B) has an ideal aperiodic autocorrelation function: Then, a pair of Golay sequences (A,B) are orthogonal themselves if they are, at least, a chip apart. So if symbols overlap, the maximum rate will raise a symbol per chip. Overlapping does not mean a high PMEPR or crest factor. Using 2n length sequences, maximum PMEPR equals 2 [Popovic 1991]. V. Diaz, GCMcom Technology

GCM (Golay Code Modulation) September 2001 GCM (Golay Code Modulation) Example: GCM 1/16 (11Mbps) 16 chips (11 Mchip/s) Data symbol Data symbol 687..5Kbps Transmission (spreading data) 1.454usec 687.5Kbps Recepcion (correlation) V. Diaz, GCMcom Technology

GCM (Golay Code Modulation)- Cont. Recepcion (correlation) September 2001 GCM (Golay Code Modulation)- Cont. Example: GCM 1/16 (11Mbps) 16 chips (11 Mchip/s) Data symbol flux 1 Data symbol Flux 2 Data symbol flux 3 Data symbol Flux 16 687.5Kbps Total: 11Mbps Data symbol Flux 16 Transmission 687.5Kbps Total: 11Mbps Recepcion (correlation) V. Diaz, GCMcom Technology

GCM (Golay Code Modulation)- Cont. September 2001 GCM (Golay Code Modulation)- Cont. OFDM is composed by N simultaneous fluxes with a rate R on each carrier so total Rate is NxR. So it is called... Orthogonal Frequency Div. Multiplex. GCM is composed by N simultaneous fluxes with rate R each, then total Rate is NxR. Example: (22Mbps GCM 2/16) - 32 fluxes of 11/16(687.5Kbps)=22Mbps. So GCM should be also called... Orthogonal Time Div. Multiplexing Correlation receiver Transmission t + - V. Diaz, GCMcom Technology

GCM as a correlation based communication technique September 2001 GCM as a correlation based communication technique LTI System Golay sequences generator [n ] N-QAM MODULATOR aN[n ] bN[n ] e[n ] DEMOD. r[n ] Efficient correlator I[n ] Q[n ] + Rra[n ] Rrb[n ] [n-no] LTI system with process delay n0 M-PAM x[n ] x[n- no] Emitter Receiver Transmission path noise r  V. Diaz, GCMcom Technology

GCM as a correlation based communication technique (cont.) September 2001 GCM as a correlation based communication technique (cont.) Each symbol is encoded by means of sequences which aperiodic autocorrelation is an ideal Krönecker delta of value N. Such a system is equivalent to a Pulse Amplitude Modulation system in which receiver noise standard deviation r is reduced by a factor of . As a result, Bit Error Rate reduces as follows: Being M the number of levels per symbol, A the maximum symbol level, and  the standard deviation of input noise. V. Diaz, GCMcom Technology

GCM processor components September 2001 GCM processor components GCM encoder data signal QASK Tx data signal GCM decoder QASK Rx V. Diaz, GCMcom Technology

Efficient Golay Generator [Popovic] September 2001 GCM encoder Same encoder for all rates (Mbps): 11, 22, 33, etc... For N=16, 2log2N = 8 additions per symbol. N-1 memory positions. Efficient Golay Generator [Popovic] The sequence a is sent on phase, and b is sent on quadrature. V. Diaz, GCMcom Technology

Efficient Golay Correlator [Popovic] September 2001 GCM decoder Same decoder for all rates (Mbps): 11, 22, 33, etc... For N=16, 4log2N = 16 additions per symbol. 2(N-1) memory positions. Efficient Golay Correlator [Popovic] V. Diaz, GCMcom Technology

Aspects to Certification September 2001 Aspects to Certification GCM should be certified under old and new rules Transmission: The Power Spectrum Reception: Robustness at the receiver Noise Processing Gain Measured with respect to a reference Interference Rejection CW Jamming Margin V. Diaz, GCMcom Technology

The Power Spectrum Similar Spectrum of actual DSSS options. September 2001 The Power Spectrum Similar Spectrum of actual DSSS options. A General QASK spectrum with chip rate 11MHz. V. Diaz, GCMcom Technology

In GCM, Information is Spread September 2001 In GCM, Information is Spread For sequences of length N, each symbol is influenced by 2N symbols. Noise is averaged. S/N ratio is reduced. Spreading should be 2N? Data received Transmitted symbols t 2N data V. Diaz, GCMcom Technology

Robustness Reference for GCM: QPSK. Processing gain. September 2001 Robustness Reference for GCM: QPSK. Processing gain. Is defined as the difference between the SNR (Es/ No) required to achieve a threshold BER or PER with the reference scheme and the SNR (Es/ No) required to achieve the same threshold BER or PER when the signal is processed. For 22Mbps, N=16: SNR (Es/ No)=-1.5dB for PER=10-2. V. Diaz, GCMcom Technology

September 2001 P.G. Comparison Scheme Rate Mod Code C. G. R. G. W.G. P.G (Mbps) (dB) (dB) (dB) (dB) Barker-1 1 BPSK Barker 0.00 13.40 2.60 16.00 Barker-2 2 QPSK Barker 0.00 10.40 2.60 13.00 CCK-11 11 QPSK CCK 2.00 3.01 2.60 7.61 PBCC-11 11 QPSK 64 state BCC 5.90 3.01 2.60 11.51 PBCC-22 22 8PSK 256 state BCC 8.10 1.76 2.60 12.46 GCM-22 22 QPSK Golay 2/16 0.00 15.05 2.60 17.65 Processing Gain = Coding Gain + Rate/Spreading Gain + Waveform/Spreading Gain Scheme Eb/No Coding PER = 10e-2 Gain Uncoded QPSK 10.5 Uncoded 8PSK 13.8 Barker 0.0 CCK-11 8.5 2.0 PBCC-11 4.6 5.9 PBCC-22 5.7 8.1 GCM-22 -4.5 -4.5=-1.5-3 (2 bits/symb) V. Diaz, GCMcom Technology

Comparison 10.5-10log10(16)= -1.5dB x September 2001 Shannon Shannon (r = 11) Barker 1 Barker 2 CCK 11 PBCC 11 PBCC 22 GCM 22 (2/16) x 10.5-10log10(16)= -1.5dB 10.5-10log10(16)=-1.5dB V. Diaz, GCMcom Technology

Continuous Wave margin September 2001 Continuous Wave margin 22Mbps GCM 2/16 has better CW margin than Barker 1Mbps. It has a higher spreading ratio: 16/11=1.6dB. Theoretically, higher immunity to Bluetooth. Further: If 802.11g needs more immunity, uses longer sequences without reducing rate: Example: N=32, (22Mbps GCM 2/32). 64 fluxes of 11/32 (343.75Kbps)=22Mbps. CW=Continuous Wave V. Diaz, GCMcom Technology

Preamble Structures: Long and Short Preambles identical September 2001 Preamble Structures: Long and Short Preambles identical 802.11 HRb LONG PREAMBLE PSDU SELECTABLE GCM Symbols 11, 22, 33, 44, 55, 66, 77, 88, 99 Mbps PREAMBLE/HEADER 192 usecs Data Payload 802.11 HRb SHORT PREAMBLE PREAM/HDR 72 BITS @ 1 Mbps PSDU SELECTABLE GCM Symbols 11, 22, 33, 44, 55, 66, 77, 88, 99 Mbps 96 usecs V. Diaz, GCMcom Technology

Preamble Structures: Ultra-short proposed preambles September 2001 Preamble Structures: Ultra-short proposed preambles 802.11 HRb LONG PREAMBLE (identical 192bits) PREAMBLE/HEADER USING GCM 11MBPS 192 BITS PSDU SELECTABLE GCM Symbols 11, 22, 33, 44, 55, 66, 77, 88, 99 Mbps 17.4 usecs Data Payload 802.11 HRb SHORT PREAMBLE (identical 72 bits) PREAM/HDR 72 BITS GCM 11 Mbps PSDU SELECTABLE GCM Symbols 11, 22, 33, 44, 55, 66, 77, 88, 99 Mbps 6.5 usecs Higher immunity to noise. Easier synchronization V. Diaz, GCMcom Technology

Throughput performance September 2001 Throughput performance Shorter preamble obviously means better throughput. Without ultra-short preambles, the throughput: 100 bytes / 22-> 192usec + PSDU=36.3 usec -> 3.5Mbps. 1000 bytes /22-> 192usec + PSDU=363 usec -> 14.4Mbps. 2346 bytes/22 -> 192usec + PSDU=853 usec -> 18Mbps. With ultra-short preambles, the throughput: 100 bytes / 22-> 6.5usec + PSDU=36.3 usec -> 18.7Mbps. 1000 bytes /22-> 6.5usec + PSDU=363 usec -> 21.6Mbps. 2346 bytes/22 -> 6.5usec + PSDU=853 usec -> 21.8Mbps. Other cases: 100/99->54.9Mbps. 2346/99 -> 95.7 Mbps. V. Diaz, GCMcom Technology

Hardware complexity of 22Mbps baseband processor September 2001 Hardware complexity of 22Mbps baseband processor RF stages: Identical elements of IEEE 802.11b for all rates. Baseband: Encoder only needs 2log2N additions (No products). Decoder only needs 4log2N additions (No products). Total resources for a 22Mbps GCM 2/16 processor: (8+16)*2*11=528M additions/sec. 45*2 memory positions. V. Diaz, GCMcom Technology

Scalability/Complexity September 2001 Scalability/Complexity How to increase rate: M levels instead of binary. Higher PEMPR but always lower than OFDM without coding. Example: M=4, K=2 pairs, results 44Mbps. 528Madd/s. K sequences instead of two. Example: K=3, binary M=2, results 33Mbps. 792Madd/s. Combination of both. Example: K=3, M=4, results 66Mbps. 792Madd/s. Then: M=8, K=3, results in 99Mbps. 792Madd/s. Encoder/decoder complexity increases only with K. V. Diaz, GCMcom Technology

Why Using GCM? Spectral efficiency over 4.5bps/Hz. September 2001 Why Using GCM? Spectral efficiency over 4.5bps/Hz. Easier scalability: Ready for future needs. Lower complexity: Lower implementation costs. Lower consumption. Higher immunity to noise: Higher range...Or lower emission power: Healthy. Better performance in Bluetooth environments. Three bands in US 2.4GHz. band. V. Diaz, GCMcom Technology

GCM offers many advantages September 2001 GCM offers many advantages Additive Gaussian noise. Does not need from FEC to improve performance. Better performance than Barker 1. It has unlimited spreading gain without reducing rate. Multipath distortion. It has, at least, the same advantages and limitations 1Mbps technique has. It uses the same chip rate. Bandwidth. Same bandwidth of actual applications. Chip rate can be reduced without reducing rate, improving multipath distortion and reducing bandwidth. V. Diaz, GCMcom Technology

September 2001 Summary Golay Code Modulation is possibly the next future option to OFDM because it has fundamental characteristics of: Simplicity. Spectral efficiency. Scalability. Lower implementation costs. Future possibilities: Increasing number of bands by means of reducing chip rate, but maintaining transmission rates. Increasing range in high rate modes. GCM Communications Technology is working to develop a high rate baseband processor prototype aiming to demonstrate a future 100Mbps wireless Ethernet equivalent. V. Diaz, GCMcom Technology