Shu (Marloon) Wang

Interference Cancellation: A Short Overview How to Broadcast Multimedia Contents? [Note] Due to the asymmetry between the uplinks and downlinks of a mobile network, there are different considerations, tradeoffs and techniques for designing each directions. In general, with the recent advance on uplink interference cancellation and management techniques, mobile network is usually limited by downlinks due inter-cell interference, especially when delay is a key part of the equation. On this blog, my focus will be on downlinks. How to evolve mobile system uplinks will be discussed in separated blogs. Mobile system design usually starts from our understanding of wireless channels and the services customers are demanding. The properties of various wireless channels can help us understand the system design limitation we are facing and the potentials we may achieve.  For example, COST 231 model, which was developed by European COST Action 231. Its variations are the most popular...

[How to Broadcast Multimedia Contents? I Introduction] [How to Broadcast Multimedia Contents? II Lessons from The Channel] [How to Broadcast Multimedia Contents? IV Hierarchical Modulation] [How to Broadcast Multimedia Contents? VI Open-Loop MIMO for BCMCS] [How to Broadcast Multimedia Contents? VII Network Layer or Steam Layer Design] [Precoded OFDM for BCMCS, 3GPP2 TSG-C NTAH C00-20080218-006R1] Though hierarchical modulations have been widely adopted for enhancing broadcast multicast services, several issues are still left for future enhancements. The first consideration is the inter-layer interference (ILI) between layers. The ILI from enhancement layer(s) to base layer(s) is not additive white Gaussian. The base-layer achievable spectral efficiency is actually dented by ILI more than expected. In addition, for example, when orthogonal frequency division multiplexing (OFDM) is employed on the carrier, there is a frequency selectivity issue on the layered transmission in fad...

[ Interference Cancellation. I. A Short Overview of Multiusr Detection ] [ Interference Cancellation: II. A Conventional Receiver Design Perspective ] [ Interference Cancellation: IV. A Blind Receiver Design Perspective ] In realities it is known to be difficult to directly and precisely estimate the signal signatures { s k : k ≠ 1} for taking advantage of well-developed optimum or conventional multiuser detection schemes. In Figure 1, the design of a linear MMSE interference cancellation receiver for CDMA systems is shown as an example. As we can see, there are at least two challenges in the implementation. The first one is you need know the signal signatures of all involved users. The second one is it requires the computation-intensive matrix inverse operation. Design challenges like these make the conventional interference cancellation methodology unattractive in practical applications. Figure 1. The challenges in employing conventional interference cancellation design. A...

[ Interference Cancellation. I. A Short Overview of Multiuser Detection ] [ Interference Cancellation: III. A Signal Subspace Perspective ] [ Interference Cancellation: IV. A Blind Receiver Design Perspective ] Introduction Interference cancellation provides a promising alternative to the conventional or optimum detectors in multiuser detection. Interference cancellation methods typically require less implementation complexity while practically o ering similar performance. The idea behind interference cancellation is to estimate the multiple access and/or multipath induced interference and then to subtract the interference estimate from the received signal. Hence, compared to other multiuser detection schemes, interference cancellation pays more attention on the estimation of the multiple access interference (MAI). Different schemes for the MAI estimation lead to different interference cancellation schemes. Actually, interference cancellation detector will cancel the interferin...

[ Interference Cancellation: II. A Conventional Receiver Design Perspective ] [ Interference Cancellation: III. A Signal Subspace Perspective ] [ Interference Cancellation: IV. A Blind Receiver Design Perspective ] [Toward Forward Link Interference Cancellation, CDMA Development Group (CDG) Technology Forum 2006] CDMA cellular network capacity is known to be interference-limited since the same spectrum is shared by many users and there exists a near-far problem due to multiple access interference (MAI). Multiuser receiver is highly regarded as one of the promising interference management techniques improving spectrum efficiency and achieving high-data rates for wireless multimedia communication. It has been intensively investigated over the last two decades and received much attention for next-generation radio access network [Andrews 05, Wang 05]. Optimum multiuser receivers and conventional multiuser receivers are known to be able to solve the near-far probl...