381 research outputs found
Scheduling of Multicast and Unicast Services under Limited Feedback by using Rateless Codes
Many opportunistic scheduling techniques are impractical because they require
accurate channel state information (CSI) at the transmitter. In this paper, we
investigate the scheduling of unicast and multicast services in a downlink
network with a very limited amount of feedback information. Specifically,
unicast users send imperfect (or no) CSI and infrequent acknowledgements (ACKs)
to a base station, and multicast users only report infrequent ACKs to avoid
feedback implosion. We consider the use of physical-layer rateless codes, which
not only combats channel uncertainty, but also reduces the overhead of ACK
feedback. A joint scheduling and power allocation scheme is developed to
realize multiuser diversity gain for unicast service and multicast gain for
multicast service. We prove that our scheme achieves a near-optimal throughput
region. Our simulation results show that our scheme significantly improves the
network throughput over schemes employing fixed-rate codes or using only
unicast communications
Growth Codes: Intermediate Performance Analysis and Application to Video
Growth codes are a subclass of Rateless codes that have found interesting applications in data dissemination problems. Compared to other Rateless and conventional channel codes, Growth codes show improved intermediate performance which is particularly useful in applications where partial data presents some utility. In this paper, we investigate the asymptotic performance of Growth codes using the Wormald method, which was proposed for studying the Peeling Decoder of LDPC and LDGM codes. Compared to previous works, the Wormald differential equations are set on nodes' perspective which enables a numerical solution to the computation of the expected asymptotic decoding performance of Growth codes. Our framework is appropriate for any class of Rateless codes that does not include a precoding step. We further study the performance of Growth codes with moderate and large size codeblocks through simulations and we use the generalized logistic function to model the decoding probability. We then exploit the decoding probability model in an illustrative application of Growth codes to error resilient video transmission. The video transmission problem is cast as a joint source and channel rate allocation problem that is shown to be convex with respect to the channel rate. This illustrative application permits to highlight the main advantage of Growth codes, namely improved performance in the intermediate loss region. © 1972-2012 IEEE
Rateless Coding for Gaussian Channels
A rateless code-i.e., a rate-compatible family of codes-has the property that
codewords of the higher rate codes are prefixes of those of the lower rate
ones. A perfect family of such codes is one in which each of the codes in the
family is capacity-achieving. We show by construction that perfect rateless
codes with low-complexity decoding algorithms exist for additive white Gaussian
noise channels. Our construction involves the use of layered encoding and
successive decoding, together with repetition using time-varying layer weights.
As an illustration of our framework, we design a practical three-rate code
family. We further construct rich sets of near-perfect rateless codes within
our architecture that require either significantly fewer layers or lower
complexity than their perfect counterparts. Variations of the basic
construction are also developed, including one for time-varying channels in
which there is no a priori stochastic model.Comment: 18 page
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