135 research outputs found
A perspective on multiaccess channels
"September 1984."Includes bibliographical references."... partial support provided by NSF under Grant NSF-ECS-8310698." "... DARPA ... Contract ONR/N00014-84-K-0357."R.G. Gallager
A perspective on multiaccess channels
Bibliography: p. [65-69]"January 1985.""Grant NSF-ECS-8310698" "...DARPA...Contract ONR/N00014-84-K-0357"R.G. Gallager
Random Access Protocols with Collision Resolution in a Noncoherent Setting
Wireless systems are increasingly used for Machine-Type Communication (MTC),
where the users sporadically send very short messages. In such a setting, the
overhead imposed by channel estimation is substantial, thereby demanding
noncoherent communication. In this paper we consider a noncoherent setup in
which users randomly access the medium to send short messages to a common
receiver. We propose a transmission scheme based on Gabor frames, where each
user has a dedicated codebook of M possible codewords, while the codebook
simultaneously serves as an ID for the user. The scheme is used as a basis for
a simple protocol for collision resolution.Comment: 5 pages, 3 figures; EDIT: A version of this work has been submitted
for publication in the IEEE Wireless Communication Letters Journa
Many-Access Channels: The Gaussian Case with Random User Activities
Classical multiuser information theory studies the fundamental limits of
models with a fixed (often small) number of users as the coding blocklength
goes to infinity. This work proposes a new paradigm, referred to as many-user
information theory, where the number of users is allowed to grow with the
blocklength. This paradigm is motivated by emerging systems with a massive
number of users in an area, such as machine-to-machine communication systems
and sensor networks. The focus of the current paper is the many-access channel
model, which consists of a single receiver and many transmitters, whose number
increases unboundedly with the blocklength. Moreover, an unknown subset of
transmitters may transmit in a given block and need to be identified. A new
notion of capacity is introduced and characterized for the Gaussian many-access
channel with random user activities. The capacity can be achieved by first
detecting the set of active users and then decoding their messages.Comment: 5 pages, 2 figures, to appear in Proceedings of ISIT 201
Channel combining and splitting for cutoff rate improvement
The cutoff rate of a discrete memoryless channel (DMC) is often
used as a figure of merit, alongside the channel capacity . Given a
channel consisting of two possibly correlated subchannels , , the
capacity function always satisfies , while there are
examples for which . This fact that cutoff rate can
be ``created'' by channel splitting was noticed by Massey in his study of an
optical modulation system modeled as a 'ary erasure channel. This paper
demonstrates that similar gains in cutoff rate can be achieved for general
DMC's by methods of channel combining and splitting. Relation of the proposed
method to Pinsker's early work on cutoff rate improvement and to Imai-Hirakawa
multi-level coding are also discussed.Comment: 5 pages, 7 figures, 2005 IEEE International Symposium on Information
Theory, Adelaide, Sept. 4-9, 200
On the Non-Coherent Wideband Multipath Fading Relay Channel
We investigate the multipath fading relay channel in the limit of a large
bandwidth, and in the non-coherent setting, where the channel state is unknown
to all terminals, including the relay and the destination. We propose a
hypergraph model of the wideband multipath fading relay channel, and show that
its min-cut is achieved by a non-coherent peaky frequency binning scheme. The
so-obtained lower bound on the capacity of the wideband multipath fading relay
channel turns out to coincide with the block-Markov lower bound on the capacity
of the wideband frequency-division Gaussian (FD-AWGN) relay channel. In certain
cases, this achievable rate also meets the cut-set upper-bound, and thus
reaches the capacity of the non-coherent wideband multipath fading relay
channel.Comment: 8 pages, 4 figures, longer version (including proof) of the paper in
Proc. of IEEE ISIT 201
- …