| 1. |
- Eriksson, Jonas, et al.
(författare)
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Complexity Reduction of Blind Decoding Schemes Using CRC Splitting
- 2012
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Ingår i: 2012 IEEE Global Communications Conference (GLOBECOM). - : IEEE. - 9781467309196 - 9781467309202 ; , s. 3731-3736
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Konferensbidrag (refereegranskat)abstract
- Blind decoding, used on control channels of some multi-user wireless access systems, is a technique for achieving adaptive modulation and coding. The idea is to adapt the modulation and coding scheme to the channel quality but instead of signaling the parameters used explicitly, the receiver blindly tries a number of fixed parameter combinations until a successful decoding attempt is detected, with the help of a cyclic redundancy check. In this paper we suggest a new method for reducing the complexity and energy consumption associated with such blind decoding schemes. Our idea is to use a mini-CRC injected early in the data stream to determine if the current decoding attempt is using the correct modulation and coding parameters. We analyze and exemplify the complexity gain of this approach and also investigate the impact of the rearrangement of the CRC scheme in terms of the probability of undetected error. The presented results for the complexity gain are promising and the impact on the error detection capability turns out to be small if any.
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| 2. |
- Eriksson, Jonas, et al.
(författare)
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On Coding of Scheduling Information in OFDM
- 2009
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Ingår i: Proceedings of the 69th IEEE Vehicular Technology Conference. - 9781424425174
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Konferensbidrag (refereegranskat)abstract
- Control signaling strategies for scheduling information in cellular OFDM systems are studied. A single-cell multiuser system model is formulated that provides system capacity estimates accounting for the signaling overhead. Different scheduling granularities are considered, including the one used in the specifications for the 3G Long Term Evolution (LTE). A greedy scheduling method is assumed, where each resource is assigned to the user for which it can support the highest number of bits. The simulation results indicate that the cost of control signaling does not outweigh the scheduling gain, when compared with a simple round-robin scheme that does not need signaling of scheduling information. Furthermore, in the studied scenario, joint coding and signaling of scheduling information over all selected users is found to be superior to separate coding and signaling for each user. The results also indicate that the scheduling granularity used for LTE provides better performance than the full granularity.
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| 3. |
- Larsson, Erik G., et al.
(författare)
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Piggybacking an Additional Lonely Bit on Linearly Coded Payload Data
- 2012
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Ingår i: IEEE Wireless Communications Letters. - : IEEE Communications Society. - 2162-2337. ; 1:4, s. 292-295
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We provide a coding scheme, by which an additional lonely bit can be piggybacked on a payload data packet encoded with a linear channel code, at no essential extra cost in power or bandwidth. The underlying principle is to use the additional bit to select which of two linear codes that should be used for encoding the payload packet, this way effectively creating a nonlinear code. We give a fast algorithm for detecting the additional bit, without decoding the data packet. Applications include control signaling, for example, transmission of ACK/NACK bits
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| 4. |
- Moosavi, Reza, 1982-, et al.
(författare)
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A Fast Scheme for Blind Identification of Channel Codes
- 2011
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Konferensbidrag (refereegranskat)abstract
- We present a fast mechanism for determining which channel code that was used on a communication link. In the proposed scheme, the receiver does not need to receive the entire data to determine the actual code. Moreover, the proposed scheme can also be used to determine the interleaving/scrambling sequence that was used at the transmitter. We investigate the performance of the scheme for some standard convolutional codes.
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| 5. |
- Moosavi, Reza, 1982-
(författare)
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Aspects of Control Signaling in Wireless Multiple Access Systems
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- From its first appearance, wireless communications has changed thelife for many people worldwide. Currently, more than half of the world's population are using wireless devices for various purposes on a daily basis. While the early wireless systems could provide simple and specific low-rate services, today's systems can support a variety of more advanced services some of which require high data rate communications. This includes for example web-browsing and streaming multimedia applications. To meet the high demands on the current systems, many technical solutions have been proposed. Many of these solutions are powerful in the sense of boosting the system performance, but on the other hand, they impose a substantial control signaling overhead on the system. The control signaling refers to sending the control information that is necessary to establish and/or maintain the connection as opposed to the payload data that is transmitted during the connection.In this thesis, we are interested in evaluating the relations between the gain of deploying new techniques and the amount of control signaling overhead they incur. Moreover we are interested in finding efficient algorithms that can potentially reduce the control signaling overhead. More specifically, we first focus on the part of the control signaling overhead that concerns sending the scheduling assignments that describe how the channel resources are allocated among the users. We compare two ways for the signaling of scheduling assignments and we will study how different parameters such as scheduling granularity impact the control signaling overhead. We also provide two schemes that reduce the control signaling overhead substantially. We then provide an algorithm for fast blind identification of channel codes. This algorithm is very useful in improving the so-called blind decoding performance. This is essential since blind decoding is used to achieve adaptive modulation and coding in the control channel of some of the wireless communication systems such as 3GPP Long Term Evolution.
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| 6. |
- Moosavi, Reza, 1982-, et al.
(författare)
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Comparison of Strategies for Signaling of Scheduling Assignments in Wireless OFDMA
- 2010
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Ingår i: IEEE Transactions on Vehicular Technology. - : IEEE. - 0018-9545 .- 1939-9359. ; 59:9, s. 4527-4542
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers transmission of scheduling information in OFDMA-based cellular communication systems such as 3GPP long-term evolution (LTE). These systems provide efficient usage of radio resources by allowing users to be scheduled dynamically in both frequency and time. This requires considerable amounts of scheduling information to be sent to the users. The paper compares two basic transmission strategies: transmitting a separate scheduling message to each user versus broadcasting a joint scheduling message to all users. Different scheduling granularities are considered, as well as different scheduling algorithms. The schemes are evaluated in the context of the LTE downlink using multiuser system simulations, assuming a full-buffer situation. The results show that separate transmission of the scheduling information requires a slightly lower overhead than joint broadcasting, when proportional fair scheduling is employed and the users are spread out over the cell area. The results also indicate that the scheduling granularity standardized for LTE provides a good trade-off between scheduling granularity and overhead.
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| 7. |
- Moosavi, Reza, et al.
(författare)
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Differential Signaling of Scheduling Information in Wireless Multiple Access Systems
- 2010
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Ingår i: Proceedings of the IEEE Global Communications Conference (GLOBECOM). - 9781424456376 - 9781424456369 ; , s. 1-6
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Konferensbidrag (refereegranskat)abstract
- This paper considers the control signaling on the downlink in wireless multiple access systems, with focus on the part of the control signaling that carries information on the user's time/frequency scheduling assignments. A new idea is presented to reduce the amount of channel resources needed for this signaling. The idea is to exploit the fact that provided that only one single user is scheduled on each channel resource, then the different users' scheduling assignments are correlated. This correlation can be exploited by encoding the scheduling information differentially. In order to recover the scheduling information, a user must then decode the scheduling information of some of the others. This is possible, because on the downlink, all users can hear the transmission by the base station so that users with a high SNR may decode the control signaling sent to users with a lower SNR. We present a practical scheme to exploit this idea. Both analytical analysis and numerical examples illustrate that the proposed technique can provide a substantial reduction in signaling traffic.
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| 8. |
- Moosavi, Reza, et al.
(författare)
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Fast Blind Recognition of Channel Codes
- 2014
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Ingår i: IEEE Transactions on Communications. - : IEEE. - 0090-6778 .- 1558-0857. ; 62:5, s. 1393-1405
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Tidskriftsartikel (refereegranskat)abstract
- We present a fast algorithm that, for a given input sequence and a linear channel code, computes the syndrome posterior probability (SPP) of the code, i.e., the probability that all parity check relations of the code are satisfied. According to this algorithm, the SPP can be computed blindly, i.e., given the soft information on a received sequence we can compute the SPP for the code without first decoding the bits. We show that the proposed scheme is efficient by investigating its computational complexity.We then consider two scenarios where our proposed SPP algorithm can be used. The first scenario is when we are interested in finding out whether a certain code was used to encode a data stream. We formulate a statistical hypothesis test and we investigate its performance. We also compare the performance of our scheme with that of an existing scheme. The second scenario deals with how we can use the algorithm for reducing the computational complexity of blind decoding process, the process that, for instance, is used by terminals in LTE for detection of control information. We propose a heuristic sequential statistical hypotheses test to use the fact that in real applications, the data arrives sequentially, and we investigate its performance using system simulations.
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| 9. |
- Moosavi, Reza, 1982-, et al.
(författare)
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Fast Identification of Control Signaling Aided by Please-Decode-Blindly (PDB) Messages
- 2012
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Ingår i: 2012 Swedish Communication Technologies Workshop (Swe-CTW). - : IEEE Press. - 9781467347624 - 9781467347617 ; , s. 53-58
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Konferensbidrag (refereegranskat)abstract
- Blind decoding of control information is used in some wireless multiple access systems such as LTE to achieve adaptive modulation and coding, as well as to address the multiple access problem on the control channel. Blind decoding incurs high computational complexity in mobile terminals. In this paper, we describe a scheme to reduce the computational complexity associated with the blind decoding. The main idea is to broadcast a "please-decode-blindly" message to all terminals that are eligible for scheduling, to instruct a subset of the terminals to perform the blind search. We propose two schemes to implement our idea and we investigate their performances via system simulations.
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| 10. |
- Moosavi, Reza
(författare)
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Improving the Efficiency of Control Signaling in Wireless Multiple Access Systems
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Prior to the transmission of payload data in any multiple access system, there is generally a need to send control information such as scheduling assignments, transmission parameters and HARQ acknowledgments. This process is called control signaling and has a significant impact on the overall system performance. This dissertation considers different aspects of control signaling and proposes some novel schemes for improving it. The dissertation is split into two parts where in the first part the focus is on the transmission of scheduling assignments, and in the second part the focus is on improving the “blind decoding” process that is used to achieve adaptive coding and modulation in transmission of control information.More specifically, in the first part of the dissertation we first compare the two conventional schemes for control signaling using extensive system simulations. In doing so, we use practical assumptions on the scheduling algorithm as well as on the compression and transmission of the scheduling information. We then provide two schemes for reducing the amount of control signaling that concerns the transmission of scheduling assignments. The first scheme, which is reminiscent of source coding with side information, uses the knowledge that each user has about its own channel condition to compress the scheduling information more effectively. The second scheme uses the fact that in wireless multiple access systems, a user with a given channel condition can in principle decode the data intended to the users that have weaker channels. Therefore, the idea is to send the scheduling information of different terminals in a differential manner starting from the user with the weakest channel and letting all the terminals overhear the transmission of one another. Finally, in the last section of this part we use some of the recent results in information theory to form a general framework for the comparison of different control signaling schemes. We formulate an optimization problem that for a given desired error probability finds the minimum required number of channel uses for a given signaling scheme.In the second part of the thesis, we propose three schemes for reducing the complexity of the blind decoding process. The first one is a novel scheme for fast blind identification of channel codes. More precisely, we propose an efficient algorithm that for a given sequence of received symbols and a given linear channel code, finds the posterior probability that all the parity check relations of the code aresatisfied. We then use this quantity to perform a sequential statistical hypotheses test that reduces the computational complexity of blind decoding. The idea in the second scheme is to broadcast a control message prior to the transmission of control information to instruct only a subset of the terminals (ideally only those terminals that have been scheduled for reception of payload data and hence benefit from performing a blind search attempt) to perform blind search decoding, which can be used for instance in LTE to reduce the complexity of the blind decoding process. Finally, in the third scheme we propose to split the CRC, used by the terminals to find their control information, into two parts and inject one part early in the control data stream so that the terminals can detect early if the current decoding attempt will be successful, which ultimately reduces the blind decoding complexity.
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