Alloyant: High Performance Broadband Wireless Networks
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Header: Mobile and Fixed broadband wireless radio access systems

Spatial Division Multiple Access - SDMA

Since StreamStar4 uses an 8-element Smart Antenna Array, it is perfectly suited to employ SDMA (Spatial Division Multiple Access) - an advanced technique that vastly improves spectral efficiency and system capacity.

All major current wireless systems operate in two main dimensions - frequency and time. Frequency-based multiplexing such as OFDMA allocates resources in the frequency domain, and framing splits the resources in the time-domain (timeslots).

StreamStar4 SDMA introduces an additional, 3rd dimension to the resource allocation plane - the spatial (space) domain. Only possible with a multi-element antenna system, SDMA can now allocate the same frequency-domain resources (subcarriers) to different users, at the same time - without causing interference. Since the subcarriers are allocated to users with a significant spatial separation, they can be active at the same time and carry different information - increasing the total system capacity.

SDMA is far superior in performance to traditional, easier to design techniques such as MIMO (Multiple Input, Multiple Output). While MIMO heavily relies on multipath, polarization and antenna diversity, SDMA has no such constraints. In addition, SDMA does not suffer from ICI (Inter-carrier Interference) which is a natural phenomenon with MIMO.

With SDMA, a StreamStar4 Base Station can achieve up to 30 Mbps of throughput in just a 5 MHz channel - for a class-leading spectral efficiency of 6 b/s/Hz.