The design of xMax MAC (aka xMAC) protocol was driven by the observation that existing MAC protocols (e.g. IEEE 802.11, WiMax, HSDPA) do not meet latency and scalability requirements for reliable voice services over wireless broadband networks. As an example, the downlink latency associated with the IEEE 802.11 (commonly known as WiFi) MAC becomes unacceptable for > 12 concurrent calls. Similarly, the downlink latency associated with the WiMax MAC with basic scheduler becomes unacceptable for > 17 calls.
Because of limitations with these and other common radio protocols, xG developed and implemented its own over the air protocol that is not based on WiFi, WiMAX or traditional cellular technology like LTE. The xMax over the air waveform has been specifically designed for use in a deterministic (i.e. fixed low latency) cognitive radio network. This waveform, in conjunction with its purpose built xMAC offers capabilities and performance not found in other wireless solutions.
xMAC supports the following functionality:
- Deterministic latency (30 msec) independent of number of concurrent calls
- Adaptable to changes in voice codec
- Support of IP and VoIP traffic (i.e. QoS, Admission Control)
The resulting xMAC is a heterogeneous MAC protocol wherein time-slot based access (TBA) is used for voice and broadband data sessions and contention based access (CBA) is employed for sending control messages while registering or handing off between xAPs.