Motorola Corporation

Alton P Werronen

Duane C Rabe

Gerald P Labedz

Kenneth A Felix

Thomas B Hart

Joseph J Schuler

Thomas G Hulsebosch

Frederick G Atkinson

Scott A Hardman

In a cellular TDMA communication system, prior to the handoff of a mobile unit (225) from a serving base-site (200) to a target base-site, (205 or 210) , the target base-site (205 or 210) establishes frame synchronization with the serving base-site (200). In this effort, first, the serving base-site timing is determined. Next, a timing difference between the serving base-site timing and a target base-site timing is calculated. Thereafter, frame positions within the serving base-site TDMA traffic channels are identified as a function of the timing difference in order to establish frame synchronization. Armed with this information, target base-sites (205 and 210) can continuously monitor all serving base-site (200) traffic channels for respective RSSI values. Preserving this information in memory enables fast and accurate signal strength determinations upon handoff.

Method for establishing frame synchronization within a TDMA

A cellular radiotelephone system transfers a call from a source base-site (200) to one target base-site (205,210). A source base-site (200) in the first RF coverage area (100) measures the signal strength (RSSI.sub.S) of a mobile (225), provides a forecasted signal strength (RSSI.sub.F) representing a would-be power increase of the mobile (225) and sets up two time windows. The source base-site (200) sends the measured and forecasted signal strengths to candidate target base-sites (205,210) found by the mobile (225) which measure the mobile (225) signal strength (RSSI.sub.T) and compare it once to RSSI.sub.S plus a hysteresis value. If RSSI.sub.T is greater than RSSI.sub.S, the call is transferred to the best responding cell. If RSSI.sub.T is below RSSI.sub.S, RSSI.sub.T is compared to RSSI.sub.F. During this time, the mobile 225 will increase power at the end of the first time window. If RSSI.sub.T is ever greater than RSSI.sub.F at any of the candidate target base-sites (205,210), the call is transferred to the responding target base-site (205,210). If the source base-site (200) receives no responses during the second time window, the process ends.

Radio telephone system incorporating multiple time periods for

A method and appartus for diversity reception in a communication system wherein at least a dual branch receiver is provided with a stored replica of expected reference information that is correlated with the received time-dispersed signals to obtain an estimate of the transmission channel's impulse response as seen by each branch, and determine, among other things, phase error between the branch local oscillators and the time-dispersed signals. Matched filters are constructed which then coherently align the time-dispersed signals from each branch with that branch's local oscillator, also constituting the first part of the equalization. The diversity processing stage may perform bit by bit selection on the re-aligned signals, maximal ratio combining of the re-aligned signals, or equal gain combining of the re-aligned signals, following each by a sequence estimation which uses similarly selected or combined channel distortion compensation parameters to complete the equalization process on the new signal. In digital modulated carrier systems, providing expected reference information eliminates the neeed for carrier recovery feedback for each branch while performing part of the equalization process.

Method and apparatus for diversity reception of time-dispersed signals

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Palatine, IL, United States of America

Alton P Werronen