Multi-beam assisted MIMO — A novel approach to fixed beamforming

Fourth-generation (4G) wireless networks promise the provision of unprecedented data rates. However apart from achieving a very high headline rate, it is also critical that future systems provide the capacity density of at least 1 Gbit/s/km² that is expected to be in demand. A promising solution that can provide the needed capacity density uses a large number of narrow beams at the base station with the aid of a Butler matrix. This fixed beamforming approach needs to be enhanced in order to provide the required capacity density as user throughput suffers from inter-beam interference because users are not likely to be located at the boresight of beams. For this purpose we propose that multiple-input multiple-output (MIMO) techniques are applied in the beam domain, resulting in a concept we may describe as multi-beam assisted MIMO (MBA-MIMO). This is shown to effectively mitigate interference and enable the provision of the required capacity density. Therefore MBA-MIMO is an attractive technology that can play a prominent role in future wireless networks beyond 4G.