RELAY STATION CAPABILITIES | IEEE 802.16J

As the standard is still evolving, it is not clear what the final variant will look like. However, at present, it appears that two categories of RS will be defined: low capability RS (simple RS) and high capability RS (full function RS). The simple RS is used for low cost deployment, and operates on one OFDMA channel. It contains no control functionality (i.e., control functions are centralized in the MMR-BS) with one transceiver and optionally supports multiple input multiple output (MIMO). The full function RS can operate on multiple OFDMA channels, implement distributed control functions, and support MIMO. This type of RS has a further two variants: fixed/nomadic full function RS and mobile full function RS. Mobile RSs add support for handover and the ability to deal with a varying channel due to mobility. Table 1 summarizes the different RSs capabilities.

Table 1: RS Capabilities 

	Simple RS	Full Function Fixed/Nomadic RS	Mobile RS
Number of OFDMA channels	1	≥1	≥1
Duplexing on MMR and access links	TDD	TDD or FDD	TDD or FDD
Frequency sharing between access and MMR links	Yes	Yes or No	Yes or No
Mobility	Centralized in MMR-BS	Centralized in MMR-BS or distributed in RSs	Centralized in MMR-BS or distributed in RSs
Antenna support	SISO or MIMO	MIMO	MIMO

At present, it is considered that an MMR network could be composed of multiple usage models including multiple RS types specifically deployed. But at present, there is only a little work about the heterogeneous functionalities of the RSs in different scenarios.

For example, an MS can move from the coverage provided inside a building by fixed/nomadic RS to a train where the coverage is provided by a mobile RS. Furthermore, there is no direct mapping between the usage models and the types of RS. An operator may deploy a variety of different RS types depending on traffic, mobility, topology (two hops or more) within the area of each RS location for a specific usage model.

In fact, the future standard will not answer all the issues raised by the RS incorporation to provide vendor differentiation. For instance, intelligent scheduling either at the BS (in a centralized approach) or at the BS and RSs (in a distributed approach) are required to minimize the interference that occurs at the RSs.