596 research outputs found
Rate-adaptive modulation for square OSTBCs in arbitrarily correlated Rayleigh fading with imperfect channel estimation
No full textMultiple-input multiple-output (MIMO) systems employing adaptive modulation have been widely used for their potential to optimize the spectral efficiency while keeping the bit error probability (BEP) under a certain target level. In this paper, we examine a MIMO system using square orthogonal spacetime block codes (OSTBCs) with rate-adaptive M-QAM and operating over arbitrarily correlated Rayleigh fading channels with imperfect channel estimation. Assuming finite-rate feedback without delay, we derive accurate closed-form expressions for the average BEP, spectral efficiency and bit error outage of our system. The presented expressions allow to easily study the impact of channel estimation errors and fading correlation on the performance of rate-adaptive MIMO OSTBC systems
Comparison of Reed-Solomon and Raptor codes for the protection of Video On-Demand on the erasure channel
No full textStreaming on-demand video services can be provided to an end user by transmitting video data as a sequence of Internet Protocol (IP) packets over the network. In order to maintain a sufficient video quality at the end user, video packets must be protected against erasures by means of a suitable form of error control. In this contribution we make a comparison of 2 classes of Forward Error Correction (FEC) codes: the Reed-Solomon (RS) codes and the Raptor codes. We present the decoding complexity analysis of these codes and compare their erasure decoding performance. For a given decoding complexity, the codewords of the Raptor code can be taken much longer than those of the RS code, because the decoding of the former code involves only XOR operations. For a performance target of less than one decoding error event in 4 hours, a video bitrate of 7.3 Mbit/s, a latency constraint of 10 seconds and a transmission overhead of 20%, equal erasure probabilities at the decoder input are allowed for the RS(254,212) code and for the Raptor code of size (8760,7300), whereas this RS code has a 12 times higher decoding complexit
Outage probability minimization for cooperative cognitive radio with best-relay selection under an average interference power constraint
No full textIn this contribution, a cognitive radio scenario is considered, where a secondary user (SU) cooperative network is allowed to transmit concurrently with a primary user (PU), provided that the resulting average interference power at the PU receiver is kept below a certain threshold. The SU network uses a selection amplify-and-forward protocol. An optimum and a low-complexity suboptimum dynamic energy allocation strategy are proposed, that minimize the link outage probability between the source node and the destination node of the SU network under an average interference power constraint. Because the interference channels from the SU nodes to the PU are affected by fast fading, the realistic assumption is made that each SU node has access to the root mean-square value (rather than the instantaneous value) of the gain of its own interference channel to the PU. We show that both dynamic allocation strategies considerably outperform the optimum static allocation strategy, and that the low-complexity dynamic allocation performs nearly as well as the optimum dynamic allocation. Finally, we confirm that our dynamic algorithms show a significant performance improvement as compared to the optimal dynamic algorithm under a peak interference power constraint
Analysis of challenge-response authentication with reconfigurable intelligent surfaces
No full textPhysical-layer authentication (PLA) mechanisms exploit
signals exchanged at the physical layer of communication
systems to confirm the sender of a received message. In this
paper, we propose a novel challenge-response PLA (CR-PLA)
mechanism for a cellular system that leverages the reconfigurability
property of a reconfigurable intelligent surface (RIS) (under
the control of the verifier) in an authentication mechanism. In
CR-PLA, the verifier base station (BS) sets a random RIS configuration,
which remains secret to the intruder, and then checks
that the resulting estimated channel is modified correspondingly.
In fact, for a message sent by an attacker in a different location
than the legitimate user equipment (UE), the BS will estimate a
different channel and the message will be rejected as fake. Such a
solution reduces the communication and computational overhead
with respect to higher-layer cryptographic authentication. We
derive the maximum a-posteriori attack when the attacker
observes a correlated channel and the reconfigurable intelligent
surface (RIS) has many elements, and the attacker transmits
to Bob either directly or through the RIS. Using a generalized
likelihood ratio test to test the authenticity at the base station
(BS), we derive approximate expressions of the false alarm
and misdetection probabilities when both the BS and the UE
have a single antenna each, while the RIS has a large number
of elements. We also evaluate the trade-off between security
and communication performance, since choosing a random RIS
configuration reduces the data rate. Moreover, we investigate
the impact of various parameters (e.g., the RIS randomness, the
number of RIS elements, and the operating signal-to-noise ratio)
on security and communication performance
Bit error rate evaluation for orthogonal space-time block codes in the presence of channel estimation errors
No full textResource allocation for multicarrier cooperative cognitive radio networks with imperfect channel state information
No full textIn this paper we consider a decode-and-forward cooperative network, which is active in the same bandwidth as a primary user network. The cooperative or secondary user network applies a dynamic resource allocation algorithm to maximize its own performance while limiting the interference caused at the primary user receivers. The main contribution of this paper is the proposition of a new accurate approximation for the outage probability, which takes into account that the channel state information available at the transmitter is imperfect and outdated. The accuracy of the approximation and the performance of the resource allocation scheme are validated through numerical simulations. © 2014 IEEE
Analytical methods to approximate the error performance of LDPC codes in wired access networks
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