To: DaveMG who wrote (603 ) 7/11/2000 10:22:14 AM From: Valueman Read Replies (1) | Respond to of 197519 An excerpt from Dr. Viterbi--read carefully:I believe the challenge in wireless service provision is to understand the nature of the traffic and the technological capabilities and tradeoffs available. There are currently two important misconceptions in the industry: A) that with digital voice, the co-existence of telephony and data services in the same spectrum are a natural consequence; B) that wider is better in the sense that efficiency grows significantly with increased bandwidth. The co-existence fallacy is in not recognizing that all bits are not created equal. Voice bits must be delivered with a common quality of service and with minimum latency for all users, no matter where they are located (near or far from a base station, in a shadowed or in a clear location). This requires allocation of disproportional resources for disadvantaged users, both in the base station and in the portable handset. With data, on the other hand, variable latencies, requirements and resources are the norm. Being able to offer variable levels of service by advanced network measurement and allocation techniques, without overly penalizing the weakest users, we can provide overall data throughputs which are more than triple the total throughput for voice. But co-mingling the voice and data service prevents us from employing such techniques and thus from achieving such improvement multiples. The second belief, that increased bandwidth makes for increased efficiency, is also overestimated. The current standard bandwidth occupancy for CDMA telephony (IS-95) is about 1.5MHz, based on a 9.6 Kbit/sec voice bit rate and a spreading factor of 128, with a resulting coded clock rate of 1.2288 MHz. The proposed "Third Generation" clock rates are either three times this number, 3.6864MHz, or alternatively 3.84MHz, both of which fit in a 5MHz allocation. We refer to this as tripling the bandwidth. The only advantage in efficiency can be that which is due to increased trunking efficiency of a larger accessing population. This may account for 5% to 10% more than the tripling afforded naturally by the bandwidth expansion. This small advantage may be more than offset by the loss in flexibility when having to allocate bandwidth in 5MHz rather than 1.5MHz segments. Furthermore, if this wider bandwidth is shared between voice and higher speed data, even this small advantage is illusory. Data service, as just noted, will require a variety of data rates depending on the user's needs, location and resources, so trunking efficiency for such a diverse population is hardly a meaningful measure, especially if, as noted, throughput can be tripled through alternate service assignment protocols. Which leads us finally to consideration of the means for enhancing throughput of data-only services. We need to recognize, first of all, that the most demanding service application is Web browsing and downloading data from the Internet. Thus the heavily loaded direction is the forward one, to the user terminal from the base station. The reverse direction, from the user to the base station, consists primarily of point-and-click commands. But even the uploading of long files, such as images or long reports, will be far less sensitive to latency than for downloading data to the user. Thus the need for the much higher throughput is not as significant for the reverse direction. In this scenario, by judicious management of latency, resources and requirements, along with some technological improvement, forward throughput can be increased by a factor of three to four times, resulting in average throughput in excess of 600 Kbits/sec and peak data rates of 2.4 Mbits/sec, all within the current CDMA bandwidth. An obvious question then is why triple the bandwidth if we can more than triple the downloading throughput in the current bandwidth allocation?