Digital cellular-its roots and its future

Cellular radio started in the early 1980s by using analog technologies. Research in voice coding, modulation, and channel coding resulted in second-generation cellular radio based on digital technologies, which were introduced in the early 1990s. These were all based on advanced time division multiple access technology, resulting in better capacity and lower cost. Today, these digital technologies-based on the Global System for Mobility, digital Advanced Mobile Phone System, and personal digital cellular-have more than 100 million subscribers worldwide. The next step is to introduce wide-band packet services for wireless Internet up to 2 Mb/s. These so-called third-generation systems (Universal Mobile Telecommunications Services, IMT2000) are planned to be introduced in the early 2000s     

Asymptotic Performance of Delayed Delta Coding with Single and Double Integration

A study of the asymptotic performance of delta coding with delayed decision is presented for the cases of first and second order integration assuming a stationary, bandlimited Gaussian source. The resulting signal-to-distortion-ratio serves as an upper bound for any delayed (multipath) decision scheme provided that the sampling rate exceeds the Nyquist rate by a factor greater than about two. The analysis shows that the improvement offered by delayed encoding relative to ordinary delta modulation has its basic origin in diminished overload distortion. Some insight is given into how the improvement is related to the decoding filter. Finally, numerical results are given for some sources with speech-like spectra     

Algorithms for Delayed Encoding in Delta Modulation with Speech-Like Signals

This concise paper is concerned with the problem of improved delta-coding by using delayed decision instead of bit-bit-by-bit decision. It is found that delayed encoding allows a fairly general predictor to be used without causing instability problems. Simulations indicate that considerable improvement can be achieved by matching the feedback filter to the input process. Delayed encoding requires a search algorithm for making the decisions. Some proposals of algorithms that are efficient from a computational point of view are presented. Particular interest is attached to a highly truncated version of the Viterbi algorithm, which seems very promising.     

Capacity of digital cellular TDMA systems

The capacity of digital TDMA (time-division multiple-access) systems is addressed. It is projected that capacity improvement will be of the order of 5-10 times that of analog FM without adding any cell sites. For example, the North American TIA (Telecommunication Industry Association) standard offers around 50 Erlang/km² with a 3-km site-to-site distance. In addition, the TDMA principle allows a faster handoff mechanism (mobile assisted handoff), which makes it easier to introduce microcells with a cell radius of about 200 m. This gives substantial additional capacity gain beyond the 5-10 factor given above. TDMA makes it possible to introduce adaptive channel allocation (ACA) methods. ACA is a mechanism that provides efficient microcellular capacity. ACA also eliminates the need to plan frequencies for cells. It is concluded that the air-interface of digital TDMA cellular may be used to build personal communication networks