Telefonaktiebolaget Lm Ericsson (Publ)

Tomas O Backstrom

Peter L Wahlstrom

Anders B Sandell

Jan-Erik Stiernvall

Gustav Larsson

Torbjorn Ward

Ragnar E Kahre

A radio-frequency receiver employing antenna diversity is provided with a plurality of antennas and a local oscillator. Individual error signals are derived from each of respective ones of signals received from the plurality of antennas. The error signals are thereafter combined in such a way as to arrive at a combined error signal having greater reliability than any one of the individual error signals taken alone. Finally, an automatic frequency control circuit is controlled using the combined error signal. Since the effect of fading on the input signal to the automatic frequency control circuit is reduced, performance of the automatic frequency control circuit is increased and the quality of radio reception is improved.

Diversity radio receiver automatic frequency control

Reception of a transmission in a radiotelephone system including an equalizer is improved by training the equalizer using a synchronization portion of the transmission having a data pattern chosen for its correlation properties and retraining the equalizer using a portion of the transmission transmitted for a different purpose. In particular, the portion of the transmission transmitted for a different purpose may be the digital verification color code transmitted during each burst in a digital cellular mobile radiotelephone system. Reception quality is increased by training the equalizer at more frequent intervals without increasing transmission overhead.

Equalizer training in a radiotelephone system

Synchronization is maintained between a regional radio transmitter/receiver and a remote transmitter/receiver communicating across a TDMA channel by detecting time misalignment of communications from the remote transmitter/receiver to the regional transmitter/receiver, commanding the remote transmitter/receiver to adjust its transmission timing, and, until the remote transmitter/receiver has adjusted its transmission timing, looking for a synchronization pattern accompanying transmissions by the remoter transmitter/receiver during two discontinuous time intervals, one centered about a time of occurrence of the synchronization pattern before the command and another centered about an expected time of occurrence of the synchronization pattern in response to the command. Effectively, what would otherwise be a disadvantageously wide time window is split into two advantageously narrow time windows to avoid detection of false syncs. Fewer false syncs are detected, and speech quality is increased.

Split-window time alignment

Signals in synchronizing sequences and data sequences are transmitted over a fading channel to a Viterbi-receiver. The signals are received by antennas and sampled to received antenna signals (s.sub.in,r (k)). Part channel estimates (h.sub.est,r) for the individual antennas are formed. For Viterbi-analysis, assumed input signals (s.sub.a,r (.DELTA.T.sub.ij,k)) for the data sequence are produced with the aid of the part channel estimates (h.sub.est,r). Part metric values (m.sub.r (.DELTA.T.sub.ij, k)) are formed as a difference between the received antenna signal (s, .sub.in,r (k)) and corresponding assumed input signals (s.sub.a,r (.DELTA.T.sub.ij, k)) for Viterbi state transitions (.DELTA.T.sub.ij). For one state transition there is formed a metric value such as the sum of a metric value ((M(T.sub.j, k-1)) for an old state (T.sub.j) at a preceding sampling time point (k-1) increased with a weighted (K.sub.r) sum of the part metric values (m.sub.r (.DELTA.T.sub.ij, k)) belonging to individual part channel estimates (h.sub.est,r). Corresponding metric values are formed for all state transitions to the new state (T.sub.i) and the smallest of these metric values is chosen in accordance with the Viterbi-algorithm.

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Kista, Sweden

Tomas O Backstrom