Optimization of Layer Selection with Unreliable RI in LTE Systems

This paper investigates the optimization of transmission spatial layer selection with unreliable rank indicator (RI) in downlink LTE systems. Taking the block error rate (BLER) into consideration, we propose an accurate throughput calculation (ATC) algorithm at user equipment (UE) side as well as at evolved NodeB (eNB) side. On the basis of ATC algorithm, we propose an accurate RI selection algorithm to periodically choose the preferred number of transmission spatial layers at UE side. Further based on acknowledgement (ACK)/ negative acknowledgement (NACK) history, channel quality indicator (CQI) is adjusted at eNB side to achieve the throughput optimal target BLER. By substituting the derived BLER into ATC algorithm, the optimal number of transmitted spatial layers in current downlink channel is derived at eNB side. Simulation results show that both the proposed CQI adjustment scheme for spatial layer selection and RI selection algorithm yield up significant throughput improvement for different evaluation scenarios in LTE systems

Optimal Control of a Single Queue with Retransmissions: Delay-Dropping Tradeoffs

A single queue incorporating a retransmission protocol is investigated, assuming that the sequence of per effort success probabilities in the Automatic Retransmission reQuest (ARQ) chain is a priori defined and no channel state information at the transmitter is available. A Markov Decision Problem with an average cost criterion is formulated where the possible actions are to either continue the retransmission process of an erroneous packet at the next time slot or to drop the packet and move on to the next packet awaiting for transmission. The cost per slot is a linear combination of the current queue length and a penalty term in case dropping is chosen as action. The investigation seeks policies that provide the best possible average packet delay-dropping trade-off for Quality of Service guarantees. An optimal deterministic stationary policy is shown to exist, several structural properties of which are obtained. Based on that, a class of suboptimal -policies is introduced. These suggest that it is almost optimal to use a K-truncated ARQ protocol as long as the queue length is lower than L, else send all packets in one shot. The work concludes with an evaluation of the optimal delay-dropping tradeoff using dynamic programming and a comparison between the optimal and suboptimal policies.Comment: 29 pages, 8 figures, submitted to IEEE Transactions on Wireless Communication

The new enhancement of UMTS: HSDPA and HSUPA

During the last two decades, the world of the mobile communications grew a lot, as a consequence of the increasing necessity of people to communicate. Now, the mobile communications still need to improve for satisfies the user demands. The new enhancement of UMTS in concrete HSDPA and HSUPA is one of these improvements that the society needs. HSDPA and HSUPA which together are called HSPA, give to the users higher data rates in downlink and uplink. The higher data rates permit to the operators give more different types of services and at the same time with better quality. As a result, people can do several new applications with their mobile terminals like applications that before a computer and internet connection were required, now it is possible to do directly with the mobile terminal. This thesis consists in study these new technologies denominated HSDPA and HSUPA and thus know better the last tendencies in the mobile communications. Also it has a roughly idea about the future tendencies

Optimum Receiver Design for MIMO Fading Channels

This thesis describes the analytical design and the performance analysis of optimum receivers for Multiple Input - Multiple Output (MIMO) fading channels. In particular, a novel Optimum Receiver for separately-correlated MIMO channels is proposed. This novel pilot-aided receiver is able to process jointly the pilot symbols, transmitted within each time frame as a preamble, and the information symbols and to decode the transmitted data in a single step, avoiding the explicit estimation of the channel matrix. The optimum receiver is designed for the following two scenarios, corresponding to different transmission schemes and channel models: 1) Narrowband Rician fading MIMO channel with spatial separate correlation; 2) MIMO-OFDM Rician fading channel with space and frequency separate correlation. For each system the performance of the optimum receiver is studied in detail under different channel conditions. The optimum receiver is compared with: - the ideal Genie Receiver, knowing perfectly the Channel State Information (CSI) at no cost; - the standard Mismatched Receiver, estimating the CSI in a first step, then using this imperfect estimate in the ideal channel metric. Since the optimum receiver requires the knowledge of the channel parameters for the decoding process, an estimation algorithm is proposed and tested. Moreover, a complexity analysis is carried out and methods for complexity reduction are proposed. Furthermore, the narrowband receiver is tested in realistic conditions using measured channel samples. Finally, a blind version of the receiver is propose

Dynamic control of wireless networks with confidential communications

Future wireless communication systems are rapidly transforming to satisfy everincreasing and varying mobile user demands. Cross-layer networking protocols have the potential to play a crucial role in this transformation by jointly addressing the requirements of user applications together with the time-varying nature of wireless networking. As wireless communications becoming an integral and crucial part of our daily lives with many of our personal data is being shared via wireless transmissions, the issue of keeping personal transactions confidential is at the forefront of any network design. Wireless communications is especially prone to attacks due to its broadcast nature. The conventional cryptographical methods can only guarantee secrecy with the assumption that it is computationally prohibitive for the eavesdroppers to decode the messages. On the other hand, information-theoretical secrecy as defined by Shannon in his seminal work has the potential to provide perfect secrecy regardless of the computational power of the eavesdropper. Recent studies has shown that information-theoretical secrecy is possible over noisy wireless channels. In this thesis, we aim to design simple yet provably optimal cross-layer algorithms taking into account information-theoretical secrecy as a Quality of Service (QoS) requirement. Our work has the potential to improve our understanding the interplay between the secrecy and networking protocols. In most of this thesis, we consider a wireless cellular architecture, where all nodes participate in communication with a base station. When a node is transmitting a confidential messages, other legitimate nodes are considered as eavesdroppers, i.e., all eavesdroppers are internal. We characterize the region of achievable open and confidential data rate pairs for a single and then a multi-node scenario. We define the notion of confidential opportunistic scheduler, which schedules a node that has the largest instantaneous confidential information rate, with respect to the best eavesdropper node, which has the largest mean cross-channel rate. Having defined the operational limits of the system, we then develop dynamic joint scheduling and flow control algorithms when perfect and imperfect channel state information (CSI) is available. The developed algorithms are simple index policies, in which scheduling and flow control decisions are given in each time instant independently. In real networks, instantaneous CSI is usually unavailable due to computational and communication overheads associated with obtaining this information. Hence, we generalize our model for the case where only the distributions of direct- and crosschannel CSI are available at the transmitter. In order to provide end-to-end reliability, Hybrid Automatic Retransmission reQuest (HARQ) is employed. The challenge of using HARQ is that the dynamic control policies proposed in the preceding chapter are no longer optimal, since the decisions at each time instant are no longer independent. This is mainly due to the potential of re-transmitting a variant of the same message successively until it is decoded at the base station. We solve this critical issue by proposing a novel queuing model, in which the messages transmitted the same number of times previously are stored in the same queue with scheduler selecting a head-of-line message from these queues. We prove that with this novel queuing model, the dynamic control algorithms can still be optimal. We then shift our attention to providing confidentiality in multi-hop wireless networks, where there are multiple source-destination pairs communicating confidential messages, to be kept confidential from the intermediate nodes. For this case, we propose a novel end-to-end encoding scheme, where the confidential information is encoded into one very long message. The encoded message is then divided into multiple packets, to be combined at the ultimate destination for recovery, and being sent over different paths so that each intermediate node only has partial view of the whole message. Based on the proposed end-to-end encoding scheme, we develop two different dynamic policies when the encoded message is finite and asymptotically large, respectively. When the encoded message has finite length, our proposed policy chooses the encoding rates for each message, based on the instantaneous channel state information, queue states and secrecy requirements. Also, the nodes keep account of the information leaked to intermediate nodes as well the information reaching the destination in order to provide confidentiality and reliability. We demonstrate via simulations that our policy has a performance asymptotically approaching that of the optimal policy with increasing length of the encoded message. All preceding work assumes that the nodes are altruistic and/or well-behaved, i.e., they cooperatively participate into the communication of the confidential messages. In the final chapter of the thesis, we investigate the case with non-altruistic nodes, where non-altruistic nodes provide a jamming service to nodes with confidential communication needs and receiving in turn the right to access to the channel. We develop optimal resource allocation and power control algorithms maximizing the aggregate utility of both nodes with confidential communication needs as well as the nodes providing jamming service