Per-user unitary rate control (PU2RC) is a multi-user MIMO technology that enhances network capacity by combining transmission pre-coding and multi-user scheduling. It builds upon single-user MIMO, which improves spectral efficiency in point-to-point wireless links, while multi-user MIMO allows a base station to communicate with multiple users simultaneously. PU2RC was first proposed in US Patent No. 7,324,480 for mobile communication systems with multi-antenna configurations. This scheme has recently been adopted in the IEEE 802.16m system description documentation and incorporated into the 3GPP LTE standard, reflecting its importance in modern wireless communication technologies.
Technology
Per-user unitary rate control (PU2RC) is a practical multi-user MIMO solution. PU2RC allows a base station to transmit different data streams to multiple users simultaneously. The base station selects target users from candidate users based on the information fed by users. Transmission data are multiplied by a pre-coding matrix selected from the set of predefined matrices before transmission. The selection of a pre-coding matrix is determined based on the information provided by users. The selection of both target users and a pre-coding matrix according to the information provided by mobiles enables the utilization of multi-user diversity and data multiplexing at the same time. Moreover, using predefined precoding matrices reduces feedback overhead from users to the base station. Pre-coding matrices used in this scheme is unitary. The use of unitary pre-coding matrices facilitates the estimation of interference from other users' data to the unintended user.
Mathematical description
The operation of PU2RC is mathematically described for the transmitter and receiver sides, respectively.
Base station
It is assumed that the base station employs N t {\displaystyle N_{t}} transmission antennas. The N t × 1 {\displaystyle N_{t}\times 1} transmission signal vector is given by
x = ∑ i = 1 K w i P i s i {\displaystyle \mathbf {x} =\sum _{i=1}^{K}\mathbf {w} _{i}P_{i}s_{i}}where w i {\displaystyle \mathbf {w} _{i}} is the N t × 1 {\displaystyle N_{t}\times 1} linear precoding vector. PU2RC generates w i {\displaystyle \mathbf {w} _{i}} based on the received finite channel status information, which is delivered to the base station from the user equipment (UE) through uplink feedback signaling. The feedback signal consists of index in a look-up table of a precoding codebook.
Receiver side
Every receiver has a receive antenna array with N r {\displaystyle N_{r}} elements. The receive signal vector at user k ( = 1 , 2 , … , K ) {\displaystyle k(=1,2,\ldots ,K)} is modeled as follows:
y k = H k x + n k {\displaystyle \mathbf {y} _{k}=\mathbf {H} _{k}\mathbf {x} +\mathbf {n} _{k}}where y k {\displaystyle \mathbf {y} _{k}} and n k {\displaystyle \mathbf {n} _{k}} are the N r × 1 {\displaystyle N_{r}\times 1} received symbol and noise, respectively, and H k {\displaystyle \mathbf {H} _{k}} is the N r × N t {\displaystyle N_{r}\times N_{t}} matrix with the channel coefficients.
Throughput performance
The figure illustrates the throughput advantage of PU2RC over the conventional single-user and no scheduling scheme, assuming that the codebook size is one, i.e., ( G = 1 ) {\displaystyle (G=1)} . For larger codebook sizes the performance can be better than the performance of the unit-size codebook. Because of codebook-based multi-user scheduling, PU2RC outperforms the conventional single-user and no scheduling scheme when the number of users is larger than one. Note that the performance plotted in the figure for the two systems were obtained assuming linear receiver.
See also
- Multiple-input multiple-output communications
- Multi-user MIMO as the advanced MIMO communication technology
- Precoding
- Spatial multiplexing
- James S. Kim, K. B. Lee, et al., Mobile communication apparatus and method including base station and mobile station having multi-antenna, US PTO 7,324,480
- S. J. Kim, H. J. Kim, C. S. Park, and K. B. Lee, "On the Performance of Multiuser MIMO Systems in WCDMA/HSDPA: Beamforming, Feedback and User Diversity," IEICE Transactions on Communications, vol. E98-B, no. 8, pp. 2161–2169, Aug. 2006.
- 3GPP TSG RAN WG1#31 R1-030354, Per unitary basis stream user and rate Control (PU2RC), 3GPP TSG-R1-030354, Tokyo, Fed 18–21, 2003. (See also R1-030130)
- Samsung, SNU, "Downlink MIMO for EUTRA," in 3GPP TSG RAN WG1 # 44/R1-060335
- Multiuser MIMO Scheme for Enhanced 3GPP HSDPA
- Kim, J.S., Hojin Kim, Yongxing Zhou, Jianjun Li, '`Multi-Mode Multi-User MIMO System with Finite Rate Feedback, IEEE Wireless Communication Systems, 2006. ISWCS '06. 3rd International Symposium on, 6–8 Sep 2006
- R. W. Heath, Jr., M. Airy, and A. J. Paulraj, "Multiuser Diversity for MIMO Wireless Systems with Linear Receivers," Proc. of the IEEE Asilomar Conf. on Signals, Systems, and Computers, pp. 1194 –1199, vol.2, Pacific Grove, California, 4–7 Nov 2001.
- A. Kogiantis and L. Ozarow, "Downlink best-effort packet data with multiple antennas," ICC'03, Volume 1, 11–15 May 2003 Page(s):715 – 719.
- K.K. Wong, R.D. Murch and K.B. Letaief, "Performance Enhancement of Multiuser MIMO Wireless Communication Systems," IEEE Transactions on Communications, Vol 50 No 12, Dec. 2002, pp 1960 –1970
- Further benefits of the revised definition of CQI for TxAA, 3GPP TSG-R1-030130, San Diego, 7–10 Jan. 2003.
Further reading
- D. Gesbert, M. Kountouris, R W. Heath Jr., C. B. Chae, T. Sälzer, From Single User to Multiuser Communications: Shifting the MIMO Paradigm
- V. Poor, Multiuser MIMO Systems
- Dr. Jacob Sharony, "Introduction to Wireless MIMO – Theory and Applications", IEEE LI, 15 November 2006
- Daniel W. Bliss, Keith W. Forsythe, and Amanda M. Chan, MIMO Wireless Communication, VOLUME 15, NUMBER 1, 2005 LINCOLN LABORATORY JOURNAL