An efficient TDMA radio link and architecture for wireless local access

A wireless digital loop architecture suitable for both portable and fixed subscribers is proposed using a low-delay 2 millisecond TDMA frame structure. This allows the elimination of echo cancelling circuits for voice applications when connecting to 2-wire transmission facilities. Each fixed radio transceiver supports up to 10 voice circuits using 32 kbps ADPCM speech coding. The resulting low-delay and high quality speech is appropriate for low-power wireless local access. For the fixed equipment, all per user baseband functions are located at central facilities to permit `shoe-box´ size radio ports or base stations. An important flexibility permitted by this TDMA architecture is low-complexity radio ports spread over a large serving area which can be connected to centralized facilities over low rate digital lines such as T-1 spans. Experimental circuits demonstrating these proposals are described