Maximising WiMAX efficiency

WiMAX is the next major method of transmitting broadband, changing the way and speed in which we connect with each other. From residential hotspots, enterprise connectivity to cellular backhaul, WiMAX will have major implications on a global scale, in both cities and developing areas.

What is WiMAX?

WiMAX, (Worldwide Interoperability for Microwave Access), is defined by a series of Institute of Electronics and Electronic Engineers (IEEE) 802.16x standards and is the accepted specification for wireless metropolitan area networks (MANs). The term WiMAX typically refers to 802.16d (sometimes referred to as 802.16-2004) which incorporates and revises 802.16, 802.16a and 802.16c.

With the increase in deployment of pre-WiMAX equipment, WiMAX is gaining considerable momentum as the technology of choice for a wide range of business models.

WiMAX and Synchronisation

As with all digital communication networks, precise synchronisation and timing is also a requirement of WiMAX. WiMAX technology supports both Frequency Division Duplex (FDD) and Time Division Duplex (TDD), each having their merits.

Voice traffic, which is relatively predictable and symmetrical, requires relatively constant bandwidth in both uplink and downlink channels. FDD, with its equal partitions, is a highly efficient wide-area coverage technology for transporting voice traffic.

Data-heavy traffic, on the other hand, tends to be highly asymmetrical in nature, with downlink traffic being far more heavily utilized than uplink and with frequent bursts of data usage quite common. The TDD single channel is completely responsive to changes in uplink/downlink demand for fully efficient usage of the available spectrum. While customers experience an always-on connection, no system capacity is utilized unless data is being transmitted or received.

Both FDD and TDD require the carrier frequency to be locked to an accuracy of 8 x 10-6. However TDD also imposes the requirement to align the phase of the uplink and downlink time slots of adjacent stations to a common time reference to avoid interference.

With reference to figure 1. The Rx-Tx transition gap (RTG) and Tx-Rx transition gap (TTG) are established between the uplink and downlink transmission frames to enable the subscriber equipment to re-orientate themselves.

figure 1.Time Division Duplex Frame Structure  

To avoid interference all adjacent stations must align their transition gaps. Obviously each transition gap effectively equates to dead bandwidth and therefore, not only is their alignment crucial but also their duration must be minimised to maximize data transfer capacity. IEEE 802.16d allows for transition gaps as small as 5 microseconds in duration.

Performance and QoS call for Precision Synchronisation

WiMAX is attracting considerable attention from network operators as an important service delivery technology in the next generation of telecommunication networks. Undoubtedly the delivery of carrier class performance and quality of service will require precision synchronisation.

Horsebridge and WiMAX Synchronisation

We are market leaders in carrier class synchronisation solutions. Working closely with the leading manufactures of WiMAX technology, we have developed our Next Generation Sync™ range, GPS based solutions which meet the exacting synchronisation requirements of WiMAX. Our Next Generation Sync units have already been deployed in the first major WiMAX rollouts and in field trails have been proven to provide optimum performance.