A Secure Information Transmission Scheme With a Secret Key Based on Polar Coding

Polar coding is the error correction coding proposed by Arikan. In polar coding, the error rate of the decoding result differs for each bit position owing to the channel polarization. In the case of polar coding with an infinite codeword length, the decoding error rate at each position of the decoded bit sequence is polarized to 0.5 or 0. Therefore, when a codeword of a sufficient length can be adopted, information bits will be decoded without errors by placing the frozen bits to bit positions where the decoding error rates are 0.5 at the transmitter. On the other hand, in the case of polar coding with a finite codeword length, the decoding error rate at each bit position takes a value between 0.5 and 0. Therefore, the decoding errors also occur at the bit positions where the information bits are placed. In this paper, we introduce half-frozen bits into polar coding. Half-frozen bits are the information bits which play roles like frozen bits. Half-frozen bits are placed at positions where errors hardly occur within the frozen bit positions as well as where errors prone to occur within the information bit positions. As half-frozen bits, a part of information bits is used after being applied another error correction coding. This improves the decoding error rates at information bit positions which result in high decoding error rates. Therefore, half-frozen bits improve the overall bit error rate (BER) performance of polar coding. Through computer simulation, we show that the polar coding with introducing half-frozen bits provides a higher error correction performance than the original polar coding.

Space-time block code (STBC) based on orthogonal design is one of the space-time coding methods to achieve multi-input multi-output (MIMO) diversity gain. STBC can provide sufficient space diversity gain, but it can not provide coding gain. Polar codes based on channel polarization are the first class of provably capacity-achieving codes with low encoding and decoding complexity. In order to improve the bit error rate (BER) performance of STBC, a concatenated scheme with Polar codes and STBC, named Polar-STBC scheme, is proposed in this paper. The BER performance of Polar-STBC system is discussed by numerical simulation under different polar code length, different polar code rates, and different coding methods of STBC. The results show that the performance of Polar-STBC has a big improvement in comparison with that using STBC only. The coding gain of Polar-STBC system is about 5dB when the BER is 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . Meanwhile, the longer code length and the lower code rate Polar codes have, the better BER performance the Polar-STBC system has. In addition, the different STBC coding methods have influence on the Polar-STBC system. The Polar-STBC system with more receiving antennas has a better BER performance in comparison with those with the same sending antennas and less receiving antennas. The coding gain of Polar-STBC system with 2 receiving antenna is 6.5dB improvement to the system with 1 receiving antenna when BER is 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and the code length is 1024.

The PSK (Pre-shared Secret Key) based method is appropriate for the IoT environment consisting of lightweight devices since this method requires less computing time and energy than the method to configure the session key based on the public key algorithm. A fundamental prerequisite for the PSK based method is that PSK should have been configured between the communication entities safely in advance. However, in case of a small sensor or actuator, no input and output interface such as keyboard and monitor required for configuration exists, so it is more difficult to configure PSK for such lightweight devices safely in the IoT environment than the previous Internet devices. Especially, normal users lack expertise in security so they face difficulty in configuration. Therefore, the default value configured at the time of manufacturing at factories is used or the device installer configures PSK in most cases. In such case, it is a matter for consideration whether all installers and manufacturers can be trusted or not. In order to solve such problem, this paper proposes a secure bootstrapping scheme, which utilizes the NFC (Near Field Communication) as an OOB (Out-Of-Band) channel, for lightweight devices with limited resources.

There is proposed a new method for deniable encryption based on commutative transformations. The method has been used to design the deniable encryption protocol resistant to the passive coercive attacks, which uses no pre-shared secret keys and no pre-exchanged public keys. The protocol begins with the stage at which the sender and receiver exchange their single-use public keys and compute the single-use shared secret key. Then, it is performed pseudo-probabilistic three-pass protocol with simultaneous commutative encryption of the fake and secret messages. Resistance of the proposed protocol to coercive attacks is provided by its computational indistinguishability from probabilistic no-key three-pass protocol used to send securely the fake message. To perform commutative encryption, it used exponentiation cipher. To provide security against active coercer, the protocol is to be complemented with procedure for authenticating the sent messages.

Motivated by the capacity-approaching property of both binary polar codes (PCs) and the multi-level coding (MLC) scheme, we consider the design of modulated PC over additive white Gaussian noise (AWGN) channels. The capability of modulated PC essentially depends on the selection of information bits set from all the virtual bit channels formed by both modulation and channel polarization. To this end, we characterize the a priori distribution density as the sufficient statistic for the bit channel of individual modulation levels formed by an MLC scheme, in which the codeword of symbols is split into parallel bits streams. According to the factor graph generated by the binary PC, we apply the density evolution (DE) for each binary modulation level. Consequently, distribution densities of every bit within the modulated codeword can be obtained and we select the most reliable bits as information bits and set the complement as frozen bits. Comprehensive simulations demonstrate the validness of this approach compared to the benchmark scheme.

A long-standing vision of backscatter communications is to provide long-range connectivity and high-speed transmissions for batteryless Internet-of-Things (IoT). Recent years have seen major innovations in designing backscatters toward this goal. Yet, they either operate at a very short range, or experience extremely low throughput. This paper takes one step further toward breaking this stalemate, by presenting PolarScatter that exploits channel polarization in long-range backscatter links. We transform backscatter channels into nearly noiseless virtual channels through channel polarization, and convey bits with extremely low error probability. Specifically, we propose a new polar code scheme that automatically adapts itself to different channel quality, and design a low-cost encoder to accommodate polar codes on resource-constrained backscatter tags. We build a prototype PCB tag and test it in various outdoor and indoor environments. Our experiments show that our prototype achieves up to 10× throughput gain, or extends the range limit by 1.8× compared with the state-of-the-art long-range backscatter solution. We also simulate an IC design in TSMC 65 nm LP CMOS process. Compared with traditional encoders, our encoder reduces storage overhead by three orders of magnitude, and lowers the power consumption to tens of microwatts.

Focusing on the low throughput of fair subcarrier allocation in cooperative OFDMA system, an improved algorithm with single subcarrier capacity threshold and cooperative power factor is proposed. In this algorithm, the users with bad channel can not occupy too many subcarrier, and the power for cooperating with other users of users with good channel is limited. Simulation results show that this algorithm can increase the total channel capacity with less loss of fairness.

In cooperative systems, users achieve spatial diversity and multihop gains by transmitting packets over multiple independent fading paths provided by their partners. Most previous works on cooperative communications focus on the physical layer aspects such as coding, modulation, and transceiver signal processing techniques. In this work, we study the advantages of user cooperation from a MAC layer perspective and devise queueing strategies to exploit cooperative gains in random access networks. Based on the conventional slotted ALOHA protocol, we propose a simple cooperative transmission mechanism for a two-user cooperative pair. We derive the two-user stability region of the proposed system and show the improvements compared to noncooperative systems. The benefits can be attributed to both physical layer cooperation, where users with good channels may relay for those with bad channels, and MAC layer cooperation, where system parameters can be chosen to enhance cooperation and reduce competition. Then, we extend the proposed strategy to a finite-user system that consists of multiple cooperative pairs. By treating each pair as a single transmission entity, we derive inner bounds for the finite-user stability region and propose a ranking system to characterize the transmission entities' relative tendency of being stable (or unstable).

In this paper, we propose to design a call admission control algorithm which schedules the channels for real time and non-real time users based on Utility function. In Long Term Evolution (LTE) 3GPP Networks, several works were done on call admission control but these works rarely considers scheduling of resources to the real time and non-real time users. The call requests are classified into new call (NC) request and handoff call (HC) request and the type of services are classified as VoIP and video. Then based upon the received signal strength (RSS) value, the channel is estimated as good channel or bad channel. Resource allocation is made for VoIP users based on traffic density. Then non-VoIP users and the non-real time users are allocated resource blocks using the channel condition based marginal utility function. When there are no sufficient resources to allocate, it allocates the resources of bad channel users there by degrading their service. Thus from our simulation results we show that this admission control algorithm provides channel quality and prioritizes the handover calls over new calls which allocates resources to all kinds of users.

In this paper, we investigate a downlink non-orthogonal multiple access (NOMA) system consisting of a base station (BS) and two users, where each user decodes its own signal through successive interference cancellation (SIC). When the signal of one user, called the weak user (WU) who has a bad channel, is being decoded, the signal of the other user, called the strong user (SU) who has a good channel, acts as interference. In an interference channel, we can increase the achievable rate by applying improper Gaussian signaling (IGS). Therefore, we apply IGS to SU, aiming to mitigate the interference. We also consider imperfect SIC at SU, which is a more general assumption for a NOMA system. For the considered NOMA system model, we derive the outage probability of each user in a closed form, provide its asymptotic expression, and obtain its diversity order. We also derive the ergodic rate of each of the two users in a closed form. We propose two algorithms to maximize the fairness of the NOMA system based on the primal decomposition method. Through simulation, we verify that our analysis is correct, and confirm that applying IGS improves the fairness of the NOMA system.

This paper addresses the medium access control (MAC) and physical (PHY) cross-layer design of a time-division multiple access protocol (TDMA) where users with good channels are allowed to relay the packets of other users with less favorable conditions. All signals are combined at the central node using signal processing tools in order to achieve diversity. The work is focused on an asymmetrical scenario where users experience different channel and queuing states. Two performance metrics are used: packet throughput and access delay. To facilitate the analysis, a packet reception model which represents more efficiently the cooperative PHY layer is also proposed. A multi-objective optimization is used to derive the boundaries of the throughput region, i.e., the set of all achievable user throughput values. Sketches of the two-user case show that the region is always convex and larger than the region of its non-cooperative counterpart. The results also show that cooperation is useful when some users with good channels experience low/medium traffic loads and thus can help other users with bad channels and higher traffic loads. Evaluation of access delay is also obtained by using the expressions of a modified TDMA system.

Polar codes are error correction codes developed by Erdal Arikan which achieves channel capacity and its reduced complexity makes it more attractive and successful. In the past several decades we are searching for some techniques which will reduce the effect of noise to a very low value so that we can reproduce the transmitted signal more accurately. Erdal Arkan come up with a new concept which known as polar codes, here we use a channel polarization concept and hence named as polar codes. The discovery of polar code is standing as a milestone in coding theory and lot of researches are carrying out on this topic. Variety of schemes have been proposed over these years for the generation, encoding and decoding of polar codes. The important area of research is the decoder section and most widely used one is successive cancellation decoder[3]. Reduced complexity is the most attractive feature with an overall encoding and decoding complexity of O(NlogN) for a block size of N, which leads to its great success. Polar code concept is used in the most promising 5G technology[10]. In this work a complete implementation of the polar Encoder and decoder is discussed with its MATLAB and Verilog implementations

Internet of Things (IoT) and direct-access Satellite IoT (SIoT) systems demand short block-length communication to accommodate brief transmissions under strict power constraints. In this context, it is critical to ensure high error correction reliability with minimal energy. One prominent candidate for Forward Error Correction (FEC) is Polar codes. Introduced by Arikan in 2009, Polar codes achieve the capacity of binary-input discrete memoryless channels through the phenomenon of channel polarization. While generalizing Polar codes to non-binary fields <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbb{GF}(q)$</tex> can yield improved performance compared to their binary counterpart at long block lengths, they fall short at short block length even when applying techniques such as frozen-bit-pattern and kernel optimization. In this paper, additional strategies are evaluated that go beyond these baseline techniques. In detail, kernel optimization is extended towards a multi-kernel approach and a joint optimization of modulation order and code rate on system level is proposed. Simulation results demonstrate that under these careful optimizations, non-binary Polar codes can indeed outperform binary Polar codes for short block length, as well, making them the optimal channel-coding choice for SIoT applications.

To reduce the computational complexity of soft-decision (SD) forward error correction (FEC), we propose a polar coding method with a low-complexity successive cancellation decoder. Polar coding induces channel polarization in which two bit-channels with lower and higher reliabilities are polarized. Only the less-reliable bit-channels are protected by SD-FEC, whereas the more-reliable bit-channels are offloaded, reducing the complexity of SD-FEC decoding. The degradation of the bit error ratio (BER) performance can be suppressed by designing the polar encoder structures for the successive cancellation decoder. We numerically demonstrate that the proposed method manages to both reduce the computational complexity by half and suppress the BER performance degradation by less than 0.6 dB, compared with the conventional method using only the SD-FEC.

Spread spectrum techniques including Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS) are used widely as a countermeasure against jamming attacks. In recent years, the DSSS based system has been used to achieve the anti-jamming systems without a pre-shared secret key. Delayed Seed-Disclosure DSSS (DSD-DSSS) is one of these systems that uses a random seed to generate multiple spreading codes to spread an original message. However, it discloses the information of a random seed in a way that it is vulnerable to the attacker. In this paper. we propose a new system that mainly focuses on concealing a random seed from the attacker by inserting it at a random position of a spreading message. We develop a new technique to identify the location of a random seed at a receiver by aligning between multiple received messages. Our evaluation and simulation results show that a receiver can obtain the position of a random seed, and then he can recover both a random seed then regenerating the spreading codes used to spread an original message.