5 research outputs found
Combinatorial Channel Signature Modulation for Wireless ad-hoc Networks
In this paper we introduce a novel modulation and multiplexing method which
facilitates highly efficient and simultaneous communication between multiple
terminals in wireless ad-hoc networks. We term this method Combinatorial
Channel Signature Modulation (CCSM). The CCSM method is particularly efficient
in situations where communicating nodes operate in highly time dispersive
environments. This is all achieved with a minimal MAC layer overhead, since all
users are allowed to transmit and receive at the same time/frequency (full
simultaneous duplex). The CCSM method has its roots in sparse modelling and the
receiver is based on compressive sampling techniques. Towards this end, we
develop a new low complexity algorithm termed Group Subspace Pursuit. Our
analysis suggests that CCSM at least doubles the throughput when compared to
the state-of-the art.Comment: 6 pages, 7 figures, to appear in IEEE International Conference on
Communications ICC 201
Compressive Demodulation of Mutually Interfering Signals
Multi-User Detection is fundamental not only to cellular wireless
communication but also to Radio-Frequency Identification (RFID) technology that
supports supply chain management. The challenge of Multi-user Detection (MUD)
is that of demodulating mutually interfering signals, and the two biggest
impediments are the asynchronous character of random access and the lack of
channel state information. Given that at any time instant the number of active
users is typically small, the promise of Compressive Sensing (CS) is the
demodulation of sparse superpositions of signature waveforms from very few
measurements. This paper begins by unifying two front-end architectures
proposed for MUD by showing that both lead to the same discrete signal model.
Algorithms are presented for coherent and noncoherent detection that are based
on iterative matching pursuit. Noncoherent detection is all that is needed in
the application to RFID technology where it is only the identity of the active
users that is required. The coherent detector is also able to recover the
transmitted symbols. It is shown that compressive demodulation requires
samples to recover active users whereas
standard MUD requires samples to process total users with a
maximal delay . Performance guarantees are derived for both coherent and
noncoherent detection that are identical in the way they scale with number of
active users. The power profile of the active users is shown to be less
important than the SNR of the weakest user. Gabor frames and Kerdock codes are
proposed as signature waveforms and numerical examples demonstrate the superior
performance of Kerdock codes - the same probability of error with less than
half the samples.Comment: submitted for journal publicatio
Asynchronous Code-Division Random Access Using Convex Optimization
Many applications in cellular systems and sensor networks involve a random
subset of a large number of users asynchronously reporting activity to a base
station. This paper examines the problem of multiuser detection (MUD) in random
access channels for such applications. Traditional orthogonal signaling ignores
the random nature of user activity in this problem and limits the total number
of users to be on the order of the number of signal space dimensions.
Contention-based schemes, on the other hand, suffer from delays caused by
colliding transmissions and the hidden node problem. In contrast, this paper
presents a novel pairing of an asynchronous non-orthogonal code-division random
access scheme with a convex optimization-based MUD algorithm that overcomes the
issues associated with orthogonal signaling and contention-based methods. Two
key distinguishing features of the proposed MUD algorithm are that it does not
require knowledge of the delay or channel state information of every user and
it has polynomial-time computational complexity. The main analytical
contribution of this paper is the relationship between the performance of the
proposed MUD algorithm in the presence of arbitrary or random delays and two
simple metrics of the set of user codewords. The study of these metrics is then
focused on two specific sets of codewords, random binary codewords and
specially constructed algebraic codewords, for asynchronous random access. The
ensuing analysis confirms that the proposed scheme together with either of
these two codeword sets significantly outperforms the orthogonal
signaling-based random access in terms of the total number of users in the
system.Comment: Journal version of work presented at 2010 Allerton Conference on
Communication, Control and Computing. Version 2 includes additional analysis
of randomly distributed user delays as well as a comparison with a matched
filter receive