Multiuser detection

Last updated

Multiuser detection deals with demodulation of the mutually interfering digital streams of information that occur in areas such as wireless communications, high-speed data transmission, DSL, satellite communication, digital television, and magnetic recording. [1] It is also being currently investigated for demodulation in low-power inter-chip and intra-chip communication. Multiuser detection encompasses both receiver technologies devoted to joint detection of all the interfering signals [2] or to single-user receivers which are interested in recovering only one user but are robustified against multiuser interference and not just background noise.

Mutual interference is unavoidable in modern spectrally efficient wireless systems: even when using orthogonal multiplexing systems such as TDMA, synchronous CDMA or OFDMA, multiuser interference originates from channel distortion and from out-of-cell interference. In addition, in multi-antenna (MIMO) systems, the digitally modulated streams emanating from different antennas interfere at the receiver, and the MIMO receiver uses multiuser detection techniques to separate them. [3] By exploiting the structure of the interfering signals, multiuser detection can increase spectral efficiency, receiver sensitivity, and the number of users the system can sustain.

Because of the mistaken belief in some quarters of the spread spectrum community that little could be gained from receivers more sophisticated than the single-user matched filter, multiuser detection did not start developing until the early 1980s. [4] Verdu [5] showed that the near-far problem suffered by CDMA was not inherent to this multiplexing technology and could be overcome by an optimum receiver that demodulates all users simultaneously. Verdu's receiver consisted of a bank of matched filters followed by a Viterbi algorithm. In the context of the capacity of the narrowband Gaussian two-user multiple-access channel, Cover [6] showed the achievability of the capacity region by means of a successive cancellation receiver, which decodes one user treating the other as noise, re-encodes its signal and subtracts it from the received signal. The same near-far resistance of the optimum receiver can be achieved with the decorrelating receiver proposed in. [7] Adaptive multiuser detectors that do not require prior knowledge of the interfering waveforms have also been proposed. [8] [9]

Related Research Articles

<span class="mw-page-title-main">Code-division multiple access</span> Channel access method used by various radio communication technologies

Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies. To permit this without undue interference between the users, CDMA employs spread spectrum technology and a special coding scheme.

In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission and a method of encoding digital data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital communication, used in applications such as digital television and audio broadcasting, DSL internet access, wireless networks, power line networks, and 4G/5G mobile communications.

In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminals connected to the same transmission medium to transmit over it and to share its capacity. Examples of shared physical media are wireless networks, bus networks, ring networks and point-to-point links operating in half-duplex mode.

A cognitive radio (CR) is a radio that can be programmed and configured dynamically to use the best wireless channels in its vicinity to avoid user interference and congestion. Such a radio automatically detects available channels in wireless spectrum, then accordingly changes its transmission or reception parameters to allow more concurrent wireless communications in a given spectrum band at one location. This process is a form of dynamic spectrum management.

Multi-carrier code-division multiple access (MC-CDMA) is a multiple access scheme used in OFDM-based telecommunication systems, allowing the system to support multiple users at the same time over same frequency band.

<span class="mw-page-title-main">Comparison of mobile phone standards</span> Wikimedia list article

This is a comparison of standards of mobile phones. A new generation of cellular standards has appeared approximately every tenth year since 1G systems were introduced in 1979 and the early to mid-1980s.

In telecommunications, a diversity scheme refers to a method for improving the reliability of a message signal by using two or more communication channels with different characteristics. Diversity is mainly used in radio communication and is a common technique for combatting fading and co-channel interference and avoiding error bursts. It is based on the fact that individual channels experience different levels of fading and interference. Multiple versions of the same signal may be transmitted and/or received and combined in the receiver. Alternatively, a redundant forward error correction code may be added and different parts of the message transmitted over different channels. Diversity techniques may exploit the multipath propagation, resulting in a diversity gain, often measured in decibels.

Radio resource management (RRM) is the system level management of co-channel interference, radio resources, and other radio transmission characteristics in wireless communication systems, for example cellular networks, wireless local area networks, wireless sensor systems, and radio broadcasting networks. RRM involves strategies and algorithms for controlling parameters such as transmit power, user allocation, beamforming, data rates, handover criteria, modulation scheme, error coding scheme, etc. The objective is to utilize the limited radio-frequency spectrum resources and radio network infrastructure as efficiently as possible.

Precoding is a generalization of beamforming to support multi-stream transmission in multi-antenna wireless communications. In conventional single-stream beamforming, the same signal is emitted from each of the transmit antennas with appropriate weighting such that the signal power is maximized at the receiver output. When the receiver has multiple antennas, single-stream beamforming cannot simultaneously maximize the signal level at all of the receive antennas. In order to maximize the throughput in multiple receive antenna systems, multi-stream transmission is generally required.

In telecommunications, dirty paper coding (DPC) or Costa precoding is a technique for efficient transmission of digital data through a channel subjected to some interference known to the transmitter. The technique consists of precoding the data in order to cancel the interference. Dirty-paper coding achieves the channel capacity, without a power penalty and without requiring the receiver to know the interfering signal.

Multi-user MIMO (MU-MIMO) is a set of multiple-input and multiple-output (MIMO) technologies for multipath wireless communication, in which multiple users or terminals, each radioing over one or more antennas, communicate with one another. In contrast, single-user MIMO (SU-MIMO) involves a single multi-antenna-equipped user or terminal communicating with precisely one other similarly equipped node. Analogous to how OFDMA adds multiple-access capability to OFDM in the cellular-communications realm, MU-MIMO adds multiple-user capability to MIMO in the wireless realm.

<span class="mw-page-title-main">Carrier interferometry</span>

Carrier Interferometry(CI) is a spread spectrum scheme designed to be used in an Orthogonal Frequency-Division Multiplexing (OFDM) communication system for multiplexing and multiple access, enabling the system to support multiple users at the same time over the same frequency band.

In radio, cooperative multiple-input multiple-output is a technology that can effectively exploit the spatial domain of mobile fading channels to bring significant performance improvements to wireless communication systems. It is also called network MIMO, distributed MIMO, virtual MIMO, and virtual antenna arrays.

<span class="mw-page-title-main">MIMO</span> Use of multiple antennas in radio

In radio, multiple-input and multiple-output, or MIMO, is a method for multiplying the capacity of a radio link using multiple transmission and receiving antennas to exploit multipath propagation. MIMO has become an essential element of wireless communication standards including IEEE 802.11n, IEEE 802.11ac, HSPA+ (3G), WiMAX, and Long Term Evolution (LTE). More recently, MIMO has been applied to power-line communication for three-wire installations as part of the ITU G.hn standard and of the HomePlug AV2 specification.

CDMA spectral efficiency refers to the system spectral efficiency in bit/s/Hz/site or Erlang/MHz/site that can be achieved in a certain CDMA based wireless communication system. CDMA techniques are characterized by a very low link spectral efficiency in (bit/s)/Hz as compared to non-spread spectrum systems, but a comparable system spectral efficiency.

Multiple-input, multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) is the dominant air interface for 4G and 5G broadband wireless communications. It combines multiple-input, multiple-output (MIMO) technology, which multiplies capacity by transmitting different signals over multiple antennas, and orthogonal frequency-division multiplexing (OFDM), which divides a radio channel into a large number of closely spaced subchannels to provide more reliable communications at high speeds. Research conducted during the mid-1990s showed that while MIMO can be used with other popular air interfaces such as time-division multiple access (TDMA) and code-division multiple access (CDMA), the combination of MIMO and OFDM is most practical at higher data rates.

Per-user unitary rate control (PU2RC) is a multi-user MIMO (multiple-input and multiple-output) scheme. PU2RC uses both transmission pre-coding and multi-user scheduling. By doing that, the network capacity is further enhanced than the capacity of the single-user MIMO scheme.

Anthony C.K. Soong is an American scientist who leads a research group at Huawei Technologies. His research interests are in statistical signal processing, robust statistics, wireless communications, spread spectrum techniques, multicarrier signaling, multiple antenna techniques, software defined networking and physiological signal processing.

Non-orthogonal frequency-division multiplexing (N-OFDM) is a method of encoding digital data on multiple carrier frequencies with non-orthogonal intervals between frequency of sub-carriers. N-OFDM signals can be used in communication and radar systems.

<span class="mw-page-title-main">Ajit Kumar Chaturvedi</span> Indian electrical engineering professor

Ajit Kumar Chaturvedi is an Indian professor and education administrator currently serving as director at IIT Roorkee. Previously, he has been the Dean (R&D), and currently Deputy Director at IIT Kanpur. He has largely contributed to waveform shaping and sequence design, MIMO systems. Recently, he has been bestowed with additional charge of director (acting) of newly established IIT Mandi.

References

  1. ↑ Sergio Verdu, "Multiuser Detection", Cambridge University Press, 1998, ISBN   0-521-59373-5
  2. ↑ Shu Wang; Sang G. Kim; Soonyil Kwon & Hobin Kim (2006). "Toward Forward Link Interference Cancellation" (PDF). San Francisco, CA: CDMA Development Group Technology Forum.{{cite journal}}: Cite journal requires |journal= (help); External link in |publisher= (help)
  3. ↑ Institute of Electrical and Electronics Engineers. Advances in multiuser detection. Ed. Michael L. Honig. New Jersey: Wiley, 2009.
  4. ↑ S. Verdu, "Wireless bandwidth in the making." IEEE Communications Magazine 38.7 (2000): 53-58.
  5. ↑ S. Verdu, Minimum Probability of Error for Asynchronous Gaussian Multiple Access Channels, IEEE Trans. on Information Theory, vol. 32, no. 1, p. 85-96, Jan. 1986.
  6. ↑ T. M. Cover, "Some advances in broadcast channels," in Advances in Communication Systems, A. Viterbi, Ed. New York: Academic Press, 1975, vol. 4, pp. 229-260
  7. ↑ R. Lupas, S. Verdu, "Linear Multiuser Detectors for Synchronous Code Division Multiple Access Channels,"IEEE Trans. Inf. Theory, vol. IT-35, no. 1, p. 123-136, Jan. 1989.
  8. ↑ M. Honig and H. V. Poor. "Adaptive interference suppression." Wireless Communications: Signal Processing Perspectives (1998): 64-128.
  9. ↑ M. Honig, U. Madhow and S. Verdú, "Blind Adaptive Multiuser Detection," IEEE Trans. on Information Theory, vol. 41, no. 4, pp. 944-960, July 1995.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.