It is suggested that low-power digital radio as an access technology could be integrated into a local exchange network to provide a ubiquitous personal communications network (PCN). High-quality tetherless communications services that could be provided by such an exchange-network-based PCN are described. A possible low-power exchange access digital radio system for providing these exchange-network based PCS services is discussed. The radio system uses a spectrum-efficient time-division multiple-access (TDMA) architecture made possible by advanced digital signal processing techniques. Control of the frequency reuse system is described, and frequency spectrum needs are indicated. >

A radio system proposal for widespread low-power tetherless communications

A low-overhead burst coherent demodulation method that jointly estimates symbol timing and carrier frequency offset and then performs diversity selection is studied. It coherently demodulates individual bursts of TDMA (time division multiple access) symbols by operating solely on random data within the burst without requiring training sequences. Its performance is robust against frequency offset between transmitter and receiver, thereby eliminating the need for a highly stable frequency reference. The performance of this demodulation method in a fading channel can be further improved by using a diversity selection technique based on a quality measure derived as part of the joint timing/frequency offset estimation process. Simulations and experiments have confirmed that two-branch diversity using this method can provide reliable speech communication using TDMA with a transmission rate of 450 kb/s for a portable radio channel with an RMS delay spread of 555 ns or less. >

Burst coherent demodulation with combined symbol timing, frequency offset estimation, and diversity selection

Go-back-N (GBN) and selective repeat (SR) protocols for automatic repeat request (ARQ) are compared in a frequency-nonselective Rayleigh fading channel. Protocols implemented in software are used in a computer-simulated fading channel to study the throughput of these protocols as a function of fading parameters, such as the mean signal-to-noise ratio (SNR), maximum Doppler frequency number of diversity branches, time-out period and round-trip delay. The purpose is to complement well-documented theoretical work in (1) providing some design considerations and (2) investigating quantitatively whether data communications combining detection-only coding, diversity, and basic ARQ protocols can offer reasonable throughput in a fading channel. Although based on a set of assumptions, the following conclusions remain valid: (1) SR is significantly superior to GBN when the fading rate is high; this advantage decreases as fading becomes slower; and (2) error detection combined with ARQ and diversity selection can provide reliable data communications in a Rayleigh fading channel. >

Comparison of two ARQ protocols in a Rayleigh fading channel

In the diversity receiver which switches between receiver branches to receive phase modulated signals, this invention can achieve a diversity effect with a circuit of simple construction which by switching between receiver branches based on relative modulation phase error, and can attain diversity effect not only against fading but also against any factor which might affect the transmission lines.

Phase likelihood comparison diversity receiver

The authors describe and show performance results for a diversity-selection technique in a frequency-selective fading portable radio channel. Diversity selection is performed by using a quality measure obtained from the demodulation process. This technique is compared to diversity selection based on power and diversity selection after channel decoding. It is found that this diversity selection technique is more effective in mitigating selective fading than a conventional technique based on power and that it performs almost as well as diversity selection after channel decoding. This diversity selection technique can be implemented at the portable handset by using only one receiver if the base station transmits in at least one time slot in addition to the communication slot. Thus, its use does not significantly increase the portable's hardware complexity. Simulations and experiments have confirmed that two-branch diversity using the proposed method can provide reliable speech communications using TDMA (time division multiple access) for a portable radio channel with RMS spread of 555 ns or less and a transmission rate of 450 kb/s. >

https://ieeexplore.ieee.org/iel2/808/2325/00064174.pdf

J.C. Chuang

Papers

A high performance diversity selection technique for TDMA portable radio communications