Switched diversity has largely fallen out of use, as it underutilizes multi-antenna resources, in favor of approaches that use multiple signals in combination and achieve higher gains for the same hardware cost.

One exception is the case of transmit diversity in client devices. When downlink requirements have motivated addition of a second antenna for MAS receive processing, but cost and power constraints preclude adding a second transmit radio chain, the second antenna can be used as a switched alternate for transmission, gaining 2-3 dB in some channel conditions.

Beam switching has seen virtually no commercial use. Drawbacks include high sensitivity to the subscriber's location within the beam and interference from users outside the beam's primary target. Attempts have been made to use beam switching concepts in "aftermarket" applications of MAS to existing sites, but with no measurable success to date given poor cost/benefit metrics.

Simple beam steering algorithms have also not seen successful use outside the laboratory. The radio environment in the world of commercial services is filled with multipath and scattering effects and non-line-of-site conditions that prevent techniques based on degree-of-arrival calculations from delivering useful results in most circumstances. If a wireless system has the radio-chain and processing hardware required to do beam steering, it is also equipped to use more advanced approaches such as AAS, so there is little point not to.

MRC (or MMSE) alone requires the same receive hardware as more advanced techniques (such as AAS or MIMO) but provides lower performance benefits - by typically 50% or more (in dBs of link budget as well as spectral efficiency). Knowledgeable customers in the current environment are recognizing the superior cost/benefit profile of the more advanced techniques, so MRC is being overtaken in the industry's collective work on the going-forward platforms.

AAS delivers typically a +10 to 15 dB traffic channel link budget improvement relative to a single-antenna architecture. In the mobile WiMAX application, its active interference management can push the achievable net spectral efficiency into the 4 bps/Hz range for loaded networks.

AAS alone on the infrastructure side provides operators with significant range benefits in the initial stages of their network's operation, and as their subscriber base grows and the network becomes interference-limited, AAS can provide significant capacity benefits (especially when used in combination with SDMA). This is ideal for operators with the flexibility to deploy MAS as they roll out their infrastructure, who see high capacity requirements coming early in their business plan, and who have tough constraints on client device costs. AAS interference mitigation benefits fall off gradually as subscriber mobility rises, but the link budget gains remain.

Separately, on the client side, AAS processing such as our A‑MAS solution for HSPA, can significantly enhance link budget (~ 15 dB) and hence data rate (~2x) for adaptive-modulation protocols that are being rolled out on existing sites — where retrofitting base stations to incorporate MAS is less practical.

SDMA delivers large gains in spectral efficiency but has no incremental link budget impact over AAS. The multiplier from spatial channels increases with base station antenna count as follows:

SDMA is most useful to operators with high capacity requirements, more limited spectrum, and tight constraints on client device costs and complexity. As with AAS and MIMO-based spatial multiplexing, the effectiveness of SDMA declines gradually with increasing subscriber mobility.

Baseline MIMO STC delivers higher link robustness, reducing fade margin by 4 to 6 dB, with little or no degradation as subscriber mobility rises. STC's effect on client data rate is indirect — the reduced fade margin (holding all else constant) will allow the use of marginally higher modulation classes, but it is not the kind of 2x spatial multiplexing gain achieved by Matrix B.

There is a catch, however, in networks loaded at all with subscribers: In the baseline implementation, STC's diversity gains come at the expense of worse co-channel interference, yielding essentially no net gain to system performance (link budget, data rate, or spectral efficiency).

Baseline STC is useful to operators who expect to see very light loading in their networks but high subscriber mobility.

ArrayComm has developed a profile-compliant extension to STC processing for the client device that addresses the loaded-network interference issue. This solution can restore 3-8 dB of link budget (depending on conditions in the network and the traffic model used for estimation), which can translates into roughly doubling the client data rate and hence overall network spectral efficiency.

Having solved the interference issue, Enhanced Matrix A represents an attractive processing mode for operators looking to support high data rates with high subscriber mobility even under high load.

Potential to double client data rates for high SINR channels. "Vanilla" version without active combining gain and interference mitigation processing is limited to short range. Most useful to operators focused on dense urban environments, where range is less of an issue, who are looking to differentiate their services through high client data rates.

ArrayComm is developing enhancements to the baseline Matrix B MIMO approach that incorporate key elements of AAS processing. In PUSC mode, this will improve the SINR envelope for Matrix B operation by ~ 6 dB, and in AMC (not supported by the current profiles) by another 10 to 15 dB. This extends the operator applicability of Matrix B to a broader class of deployments.

The performance of CSM in a loaded network is expected to be significantly lower than Enhanced Matrix B or SDMA because of the inadequate channel state information (i.e. pilots) incorporated in the CSM approach.

ArrayComm's ranging extension solution for WiMAX provides a ~6 dB improvement in ranging channel link budget. This enables successful and practical use of all the traffic-channel range gains identified above.