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To: Caxton Rhodes who wrote (7947)	10/29/2000 1:39:05 AM
From: ehopper	Read Replies (2) \| Respond to of 34857

The big question is whether HDR (as defined by Qualcomm for example) will ever be hit the data rates consistently in a real network. I have read thru their white paper on HDR. There has been talk of 5.2 Mbps speed at 1.25 MHz and 15 Mbps at %Mhz. However I have my doubts that these rates would be available in a practical sense within a network. HDR: Currently HDR can provide a peak rate of 2.4576 Mbps on a 1.25 MHz channel (chip rate 1.2288 MHz).This is using a modulation technique familiar to TDMA called QAM (Quadraphase Amplitude Modulation) rather than the more familiar Quadraphase Shift Keying (QPSK) in CDMA IS-95 and CDMA20001X. The reason why 16QAM boosts the rate is that it sends 4 bits of data for every Hz or bit time. This requires I believe a walsh code length of 2 which means that a maximum of 4 people per RF channel can be allocated this rate at any given time so the service providers of course would limit the full access speed time and hence the average speed is lower. Also since 16QAM requires a 9 dB signal to noise ratio again it leads to average speeds a bit slower however still above 300 Kbps in the real world. Note: A 9 dB SNR is not practical in many real , "noisy" networks. Hence re-transmissions and slower thru-put. Qualcomm's own white paper shows the mean rate at above 350kbps for HDR (Bell curve) Now for these HDR rates of 5.2 Mbps and 15 Mbps I have heard talk of in the future I can only speculate: Guess 1: The 5.2 MBps could in theory be acheived by: 1) perhaps they are using 32 QAM? This would be a first. This allows you to send 5 bits of data for every Hz but that would not hit the rate. It would have to be 64 QAM or 64 PSK Which would be very experimental and even more prone to noise. 2) reducing the walsh code to length to 1. This would in effect double the data rate but effectively elimiate all other users off of the RF channel. It would also require alot of output power to overcome the noise (less error correction) so probably not practical. 3) Maybe do all or part of #2 (or none) and offer multiple RF channels to a user. There is nothing to stop a service provider from offering more channels to a user (up to the limit of the receiver) if the service provider wishes to do so. Hence they can raise the walsh code length (thus improving noise immunity) and give the user multiple RF channels to achive 5 Mbps (just charge them for it). As for the 15 Mbps, they mention that in 5 MHz channels they can provide this. 1.25 MHz x 3 is approximatley 5 MHz so multiply by 3. I have my doubts that HDR will provide the data rates that are being talked about for the average user. OFDM etc may be the way to goif they can get the technology down to handset size. ed.