Hideichi Sasaoka

Wireless secret key generation exploiting reactance-domain scalar response of multipath fading channels

We describe a secure communication scheme that uses the random fluctuation of the natural environment of communication channels. Only the transmitter and the receiver share the communication channel characteristics. From reciprocity between a transmitter and a receiver, it is possible for them to share one-time information of their fluctuating channel. This can provide a secret key agreement scheme without key management and key distribution processes. In this paper, we propose a new secret key generation and agreement scheme that uses the fluctuation of channel characteristics with an electronically steerable parasitic array radiator (ESPAR) antenna. This antenna, which has been proposed and prototyped, is a smart antenna designed for consumers. Using the beam-forming technique of the ESPAR antenna, we can increase the fluctuation of the channel characteristics. From experimental results, we conclude that the proposed scheme has the ability to generate secret keys from the received signal strength indicator (RSSI) profile with sufficient independence.

An implementation of a CMA adaptive array for high speed GMSK transmission in mobile communications

The hardware implementation of an adaptive array as a technique for compensating multipath fading in mobile communications is described. The number of the antenna elements is four. The target communication system is modulated by 256 kbps Gaussian-filtered minimum shift keying (MSK) and has a time-division multiplexing (TDM) architecture with 24 time slots. Based on the digital beamforming concept, all of the signals and the array weights are digital-signal processed. The constant modulus algorithm (CMA) is employed for weight optimizing. In an additive white Gaussian noise channel, this system has 5.6-dB gain in an energy-per-bit-to-noise-density ratio at a bit error rate (BER) of 1.0*10/sup -3/, compared with a single antenna system. The result of the basic field test shows that the gain at a BER of 1.0*10/sup -3/ reaches 22.3 dB in a nonselective, slow Rayleigh fading channel given a 5 Hz maximum Doppler shift. >

Performance of modulation-level-controlled adaptive-modulation under limited transmission delay time for land mobile communications

The performance of an adaptive-modulation/time division duplex (TDD) scheme to support constant-bit-rate services under transmission delay time constraint conditions is evaluated in this paper. According to the received signal conditions, the modulation levels or transmission modes are selected from transmission-off, QPSK, 16QAM, or 64QAM by using the reciprocity of the propagation path characteristics in the TDD systems. Moreover, the transmission delay time is limited to keep data transmission rate constant by the memory buffer. The received signal condition is estimated by using extrapolation of pilot symbol or estimated received signal distortion at the decision stage. The performance is evaluated by computer simulation in case of 32 ksymbol/s transmission and is compared with the performance of conventional trellis-coded (TCM) 32QAM. The results show that the proposed method improves the BER performance and delay spread immunity of a system transmitting data at a constant rate under multipath fading conditions and the performance is better than that of TCM-32QAM in Rayleigh fading conditions with small Doppler frequency.

Physical-Layer Secret Key Agreement in Two-Way Wireless Relaying Systems

We consider secret key agreement based on radio propagation characteristics in a two-way relaying system where two legitimate parties named Alice and Bob communicate with each other via a trusted relay. In this system, Alice and Bob share secret keys generated from measured radio propagation characteristics with the help of the relay in the presence of an eavesdropper. We present four secret key agreement schemes: an amplify-and-forward (AF) scheme, a signal-combining amplify-and-forward (SC-AF) scheme, a multiple-access amplify-and-forward (MA-AF) scheme, and an amplify-and-forward with artificial noise (AF with AN) scheme. In these schemes, the basic idea is to share the effective fading coefficients between Alice and Bob and use them as the source of the secret keys. The AF scheme is based on a conventional amplify-and-forward two-way relaying method, whereas in the SC-AF scheme and the MA-AF scheme, we apply the idea of physical-layer network coding to the secret key agreement. In the AF with AN scheme, the relay transmits artificially generated noise, as well as channel information signal, in order to conceal the latter. Simulation results show that the MA-AF scheme outperforms the other schemes in Rayleigh fading channels, whereas the AF with AN scheme is suitable for Rician fading channels.

BER performance of CMA adaptive array for high-speed GMSK mobile communication-a description of measurements in central Tokyo

This paper describes the performance of an adaptive array as a countermeasure to multipath fading for a 256 kbps Gaussian-filtered minimum shift keying (GMSK) mobile communication system operating in the 1.5 GHz band. An adaptive array having four antenna elements is implemented using the digital beam forming concept. The constant modulus algorithm (CMA) is employed for the adaptation process to ease the implementation. Measurements in central Tokyo of the bit error rate (BER) performance and an array pattern arising in the multipath environment are presented. Analysis of the array pattern confirms that the array succeeds in directing nulls to the delayed signals. BER performance shows an improvement in E/sub b//N/sub 0/, compared with that of a single antenna system, of 17.5 to 22 dB at a BER of 1.0*10/sup -2/ in a frequency-selective fading channel. >

Cochannel interference reduction and path-diversity reception technique using CMA adaptive array antenna in digital land mobile communications

This paper describes a cochannel interference (CCI) reduction and path-diversity reception technique using a constant modulus algorithm (CMA) adaptive array antenna in digital land mobile communications. In this technique, the incident signals are individually recovered by using a multistage constant modulus (CM) array that consists of a multistage cascade of signal recovering and canceling processes. The recovered signals are sorted into the desired signal and CCI signal, and then the desired signals are combined in order to obtain the path-diversity gain, Performance is evaluated for a Gaussian filtered minimum shift keying signal and /spl pi//4-shifted quadrature phase-shift keying signal. Each signal processing is carried out using block demodulation (e.g., CMA adaptive signal recovering process and signal canceling process). Computer simulation results show that CCI can be reduced efficiently for a high-bit-rate time-division multiple-access system for quasi-static and fading channel conditions and that the bit error rate (BER) performance is improved by combining the desired signals. The extent of the improvement in BER performance indicates the difference in diversity gain between maximal ratio combining and selective combining. This suggests that a CMA adaptive array antenna is equivalent to selective combining diversity reception.

Adaptive key generation in secret key agreement scheme based on the channel characteristics in OFDM

In this paper, we proposed an adaptive key generation based on the channel characteristics in OFDM mobile radio. We have shown that DCT-based preprocessing can remove the redundancy of the channel response and it also reduces the error in the key candidate. The simulation results show that the proposed adaptive key generation realizes high-level key agreement securely by combining the preprocessing and the error detecting method.

A Scheme of Private key Agreement Based on Delay Profiles in UWB Systems

Schemes of private key agreement based on channel characteristics have been proposed for countermeasure against eavesdropper in radio communication systems using carrier modulation. This paper proposes a new scheme of private key agreement for UWB system using impulse waves. Because it is generally difficult to apply the conventional schemes to UWB system where no carrier is used. The proposed scheme employs the differences of arrival time among the direct wave and the delayed waves, which are measured at both authorized radio stations changing the transmission and reception. The proposed scheme also employs the countermeasure for the detection error of the delayed waves which differ the arrival times at both radio stations. Computer simulations are carried out to evaluate the performance of the proposed scheme in wireless PAN environments. The results of the computer simulations show that the proposed scheme can achieve key agreement without errors at signal-to-noise ratio of about 22 dB.

Block coded 16 QAM-TDMA cellular radio system using cyclical slow frequency hopping

A TDMA cellular system using cyclical slow frequency hopping and a block-coded quadrature amplitude modulation (QAM) is presented. The QAM scheme reduces the required bandwidth for voice channels. The combination of frequency hopping and coding offers immunity against multipath fading and interference. The sectorization and voice activity are used to reduce cochannel interference. These techniques increase the frequency reuse factor. The proposed system can achieve a capacity increase 13 times greater than that of analog systems.<<ETX>>

A secret key agreement scheme with multi-level quantization and parity check using fluctuation of radio channel property

As a countermeasure for eavesdroppers in wireless communication, a secret key agreement scheme using a variable directional antenna named ESPAR antenna was developed. In this paper, we describe an improved key generation method using multi-level quantization and parity check in the secret key agreement scheme. It enhances key agreement probability in legitimate parties efficiently without reducing the security. There was a trade-off between the key agreement probability and the security. Simulation result shows that the proposed method realizes higher security than the conventional one in the key agreement system using ESPAR antenna.