Abstract: In a TDM/TDMA digital radio communications system, each portable unit in accessing the system must select the "best" port through which to route each call. The so called "best" port may not, however, have an idle time-slot to accommodate the call. Attempts to route a call through a busy "best" port, or busy "second best" port will decrease the throughput of the network and result in increased call setup time. An autonomous selective routing scheme is described which increases system throughput and decreases call setup time. When a user at a portable unit (301) desires to access the network, the portable unit scans (308, 309) the downlink frequencies associated with each of the ports in the system. For each port, the portable measures signal quality (310) and determines from the received bit patterns (313) whether the port has an idle time-slot.

Abstract: To assign and coordinate radio frequencies at the fixed ports (30, 40, 50, 70) of a frequency-reusing radio communications system (5), most existing methods require pre-engineering or impose high complexity in system controller and port hardware. A simple autonomous procedure performed by each port to determine its own transmitting frequency and corresponding receiving frequency is disclosed. This procedure consists of signal strength measurements and an algorithm which selects the frequency with minimum interference from other ports. In particular, a port turns off (202) its own transmitter (306) and scans (203) all the candidate transmitter frequencies and measures (312) signal powers form the other ports. The frequency channel with the lowest received power is tentatively assigned (204) for downlink transmission by that port. This procedure is repeated by all the ports either independently and asynchronously or with a coordinated schedule.

Abstract: In order to correctly demodulate a received sequential burst of symbols in a time division multiplexed/time division multiple access (TDM/TDMA) portable radio digital telephony communications system, proper timing of the sampling time in each received symbol of the burst is necessary. In addition, in order to compensate for component drift, an estimate of the frequency offset between transmitting and receiving units is also required. A method and circuitry for estimating symbol timing and frequency offset is disclosed in which the IF radio signal is sampled and digitized at a sampling rate which is sixteen times the symbol rate. The digitized samples are processed to obtain phase values. A one symbol delay is introduced and differential phase values derived, a differential phase value being derived for each of the sixteen sampling times per symbol. The differential values are collapsed into one quadrant in the phase plane and then expanded back to the full plane.

Abstract: Coherent phase recovery in a time division multiple access (TDMA) system can be attained in a novel manner. After symbol-timing and frequency-offset are estimated, the stored received phase at the desired sampling instant is gated from memory and fed to the input of the carrier phase recovery circuitry. During a first half portion of a burst, the first half portion of the burst is stored, while the loops acquire lock. The first half portion is then fed to one of the loops in a reverse order of its reception. Demodulation is initiated as a common state of both loops in a mid-portion of the signal burst. The previously stored first half portion is backwardly demodulated by one of the loops, while the other loop demodulates the second half portion of the burst. The whole burst is recovered by storing the demodulated first and second half portions in random access memory, and then reordering the stored demodulated burst by reading the memory backwards for the first portion.