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A practical transmit beamforming strategy for closed‐loop MIMO communication
Cho, Sunghyun,Hwang, Insoo,Tarokh, Vahid,You, Cheolwoo John Wiley Sons, Ltd 2012 International Journal of Communication Systems Vol.25 No.8
<P><B>SUMMARY</B></P><P>A new beamforming strategy is proposed for multiuser systems with <I>N</I> transmit antennas at the transmitter and <I>M ⩽ N</I> single antenna receivers. The proposed scheme remarkably improves on the classical spatial division multiple access, and achieves the same data rates as spatial multiplexing for all users but with significantly superior performance/diversity gain. When compared with the Bell labs layered space–time system, the symbol rate is the same and the performance is much superior because of the presence of diversity gain. In addition, unlike the Bell labs layered space–time system, the receivers do not need to know each other's vector channels. Finally, the proposed algorithm is based on dirty‐paper coding, but does not require much complexity and is implementable. Copyright © 2011 John Wiley & Sons, Ltd.</P>
Bi-Directional Half-Duplex Relaying Protocols
Kim, Sang-Joon,Devroye, Natasha,Tarokh, Vahid The Korea Institute of Information and Commucation 2009 Journal of communications and networks Vol.11 No.5
The bi-directional relay channel is the natural extension of a three-terminal relay channel where node a transmits to node b with the help of a relay r to allow for two-way communication between nodes a and b. That is, in a bi-directional relay channel, a and b wish to exchange independent messages over a shared channel with the help of a relay r. The rates at which this communication may reliably take place depend on the assumptions made on the relay processing abilities. We overview information theoretic limits of the bi-directional relay channel under a variety of conditions, before focusing on half-duplex nodes in which communication takes place in a number of temporal phases (resulting in protocols), and nodes may forward messages in four manners. The relay-forwarding considered are: Amplify and forward (AF), decode and forward (DF), compress and forward (CF), and mixed forward. The last scheme is a combination of CF in one direction and DF in the other. We derive inner and outer bounds to the capacity region of the bi-directional relay channel for three temporal protocols under these four relaying schemes. The first protocol is a two phase protocol where a and b simultaneously transmit during the first phase and the relay r alone transmits during the second. The second protocol considers sequential transmissions from a and b followed by a transmission from the relay while the third protocol is a hybrid of the first two protocols and has four phases. We provide a comprehensive treatment of protocols in Gaussian noise, obtaining their respective achievable rate regions, outer bounds, and their relative performance under different SNR and relay geometries.
Bi-Directional Half-Duplex Relaying Protocols
Sang Joon Kim,Natasha Devroye,Vahid Tarokh 한국통신학회 2009 Journal of communications and networks Vol.11 No.5
The bi-directional relay channel is the natural extension of a three-terminal relay channel where node a transmits to node b with the help of a relay r to allow for two-way communication between nodes a and b. That is, in a bi-directional relay channel, a and b wish to exchange independent messages over a shared channel with the help of a relay r. The rates at which this communication may reliably take place depend on the assumptions made on the relay processing abilities. We overview information theoretic limits of the bi-directional relay channel under a variety of conditions, before focusing on half-duplex nodes in which communication takes place in a number of temporal phases (resulting in protocols), and nodes may forward messages in four manners. The relay-forwarding considered are: Amplify and forward (AF), decode and forward (DF), compress and forward (CF), and mixed forward. The last scheme is a combination of CF in one direction and DF in the other. We derive inner and outer bounds to the capacity region of the bi-directional relay channel for three temporal protocols under these four relaying schemes. The first protocol is a two phase protocol where a and b simultaneously transmit during the first phase and the relay r alone transmits during the second. The second protocol considers sequential transmissions from a and b followed by a transmission from the relay while the third protocol is a hybrid of the first two protocols and has four phases. We provide a comprehensive treatment of protocols in Gaussian noise, obtaining their respective achievable rate regions, outer bounds, and their relative performance under different SNR and relay geometries.
An Empirical Indoor Path Loss Model for Ultra-Wideband Channels
Ghassemzadeh, Saeed-S.,Greenstein, Larry-J.,Kavcic, Aleksandar,Sveinsson, Thorvardur,Tarokh, Vahid The Korea Institute of Information and Commucation 2003 Journal of communications and networks Vol.5 No.4
We present a statistical model for the path loss of ultrawideband (UWB) channels in indoor environments. In contrast to our previously reported measurements, the data reported here are for a bandwidth of 6GHz rather than 1.25GHz; they encompass commercial buildings in addition to single-family homes (20 of each); and local spatial averaging is included. As before, the center frequency is 5.0GHz. Separate models are given for commercial and residential environments and, within each category, for lineof sight (LOS) and non-line-of-sight (NLS) paths. All four models have the same mathematical structure, differing only in their numerical parameters. The two new models (LOS and NLS) for residences closely match those derived from the previous measurements, thus affirming the stability of our path loss modeling. We find, also, that the path loss statistics for the two categories of buildings are quite similar.