PRESENT–FUTURE TECHNOLOGIES

Over the last two years IEEE 802.16-2004 products have become more widely used and with several deployments in the field, basic experience with WiMAX technology has been increased. The new, upcoming IEEE 802.16e, which is an amendment to the IEEE 802.16-2004 standard, promises significant improvements. The major enhancements in WiMAX technology for the upcoming version of the standard are outlined in Table 1.

Table 1: Evolution of IEEE 802.16 Technology 

Technology	IEEE 802.16d	IEEE 802.16e	IEEE 802.16j
Range (km)	0.7	1.8	2 (per hop)
AAS	–	STC/MRC/SM/BF	Cooperation
Air-interface	OFDM	OFDMA	Relay-based
QoS	Basic	E-rtPS	Enhanced
Profile	IP Padios	ASN	ASN
Scenarios	Nomadic	Mobile	Mobile relaying

The most important enhancement concerns the system gain, which is roughly increased by 15–25 dB, and hence the cell range is also increased. For fixed/nomadic terminals it is evident that 802.16e is much more efficient and is also capable of catering for mobile terminals. Another decisive improvement is the introduction of AAS, which increases robustness through STC, MRC, and spectral efficiency through spatial multiplexing (SM) and BF. The transition to OFDMA clearly boosts the radio resource management efficiency and improves QoS particularly in the presence of VoIP service. It is evident that the evolution of WiMAX targets three objectives: to increase the system gain and reach customers inside their homes/offices and on the move, to boost capacity so as to reduce service costs and be competitive with other access technologies, and finally to coexist in a seamless manner in the upcoming all IP networks.

This is clearly the case with the development IEEE 802.16j which introduces the concept of relays. A relay-based network can in principle extend the range boundlessly, however, in practice 2-hop links are more likely to be implemented (for delay and throughput issues). From the designer’s perspective if the first link (BS-relay) is line of sight then the system range can be several times higher than conventional systems, and hence for coverage-limited networks the dimensioning would result in much reduced costs. Furthermore, if the BS employs BF toward the relays, concurrent communication with several of them may be established in the form of spatial-division multiple access (SDMA), therefore boosting cell capacity.

While the all IP architecture is on the way (access service network (ASN) gateway), with major manufacturers of network products supporting this direction, the next WiMAX standard, IEEE 802.16m is also under consideration. IEEE 802.16m will revise the air-interface in the scope of international telecommunications union–radiocommunication sector (ITU-R) requirements for IMT-2000 and IMT-Advanced.