US 5,396,541 A · Call handoff in a wireless telephone system

Abstract

Signaling a mobile unit to transmit a synchronization pattern with voice information upon detecting from the signal strength of the wireless mobile unit by a base station that the mobile unit is approaching a minimum threshold. Where the voice information is initially being transmitted in a set of frequency hopping channels using spread spectrum transmission, the synchronization pattern is transmitted in one or more of the set of frequency hopping channels. In addition, the base station alerts a system controller to this fact, and the system controller requests that neighboring base stations monitor the set of frequency hopping channels being transmitted by the mobile unit. In order to synchronize to the mobile unit, the base stations utilize the synchronization pattern to come into synchronization with the mobile unit. The system controller transfers the wireless mobile unit to the base station which is receiving the strongest signal strength.

Claims8

Dependent claims

A method of controlling a transfer of a wireless mobile unit from a first one of a plurality of wireless base stations to a second one of the plurality of wireless base stations in a wireless system and the wireless system having a switching controller and voice information is communicated between the wireless mobile unit and the first and second ones of wireless base stations is transmitted in an individual set of frequency channels, the method comprises the steps of:

detecting the need for a transfer of the wireless mobile unit by the first one of the wireless base stations and transmitting a transfer request message to the switching controller;
transmitting initiate transfer messages to the wireless base stations by the switching controller in response to the transfer request message;
signaling the wireless mobile unit to start transmission of synchronization information in a subset of the individual set of the frequency hopping channels with remaining frequency hopping channels transmitting the voice information by the first one of the wireless base stations in response to one of the initiate transfer messages;
synchronizing to the wireless mobile unit using the synchronization information by the remaining ones of the wireless base stations in response to the initiate transfer messages;
measuring the signal strength of the wireless mobile unit by each of the wireless base stations and transmitting the signal strength measurements to the switching controller by each of the wireless base stations;
and
selecting the second one of the wireless base stations to receive the transfer of the wireless mobile unit from the first one of the wireless base stations by the switching controller in response to the signal strength measurements received from the wireless base stations.

4 more elements

An apparatus for controlling a transfer of a wireless mobile unit from a first one of a plurality of wireless base stations which is communicating a call with the wireless mobile unit in a wireless system and the wireless system having a switching controller and voice information is communicated between the wireless mobile unit and the first and second ones of wireless base stations is transmitted in an individual set of frequency channels, the apparatus comprises:

means in the first one of the wireless base stations for detecting the need for a transfer of the wireless mobile unit and transmitting a transfer request message to the switching controller;
means in the switching controller for transmitting initiate transfer messages to the wireless base stations in response to the transfer request message;
means in the first one of the wireless base stations for signaling the wireless mobile unit to start transmission of synchronization information in a subset of the individual set of the frequency hopping channels with remaining frequency hopping channels transmitting the voice information in response to one of the initiate transfer messages;
means in the remaining ones of the wireless base stations for synchronizing to the wireless mobile unit using the synchronization information in response to the initiate transfer messages;
means in each of the wireless base stations for measuring the signal strength of the wireless mobile unit and transmitting the signal strength measurements to the switching controller, and
means in the switching controller for selecting a second one of the wireless base stations to receive the transfer of the wireless mobile unit from the first one of the wireless base stations in response to the signal strength measurements received from the wireless base stations.

3 more elements

Dependencies are inferred from the claim text.

Call handoff in a wireless telephone system

Life of this patent

Call handoff in a wireless telephone system

Life of this patent

Abstract

Claims8