Hisato Iwai

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.

An investigation of space-path hybrid diversity scheme for base station reception in CDMA mobile radio

In CDMA mobile radio communication systems, degradation of instantaneous signal to interference power ratio (C/I), which causes impairment of frequency utilization factor, will be significant in multipath fading environments. In this paper, a hybrid diversity scheme for fading reduction combining effects of space diversity and path diversity (represented by the RAKE method) is investigated. A quantitative evaluation of fading reduction effects of the hybrid diversity is performed, comparing them with those of space diversity only and path diversity only. The hybrid diversity scheme is promising in environments where the delay spread of a transmission path is 1 /spl mu/s or less. >

Modeling of signal envelope correlation of line-of-sight fading with applications to frequency correlation analysis

Based on the theoretical method developed by Clarke for the analysis of correlation characteristics in Rayleigh fading conditions, we develop a general model for envelope correlation statistics of line-of-sight fading known as Nakagami-Rice fading. The model developed here has a considerable degree of univer- sality and can be applied to the analysis of correlation statistics in frequency and spatial domains for microcellular mobile radio, maritime and aeronautical mobile-satellite communications. Us- ing this model, we examine the frequency correlation statistics of two typical Nakagami-Rice fading environments.

The equivalent transmission-path model-a tool for analyzing error floor characteristics due to intersymbol interference in Nakagami-Rice fading environments

Land mobile radio systems such as car telephones and handy personal terminals used outdoors have enjoyed a remarkable evolution. To design reliable mobile radio systems, however, it is vital to have a good understanding of the impact of wave propagation characteristics on digital transmission quality in a wide variety of mobile radio environments. A very simple but general scheme for calculating irreducible bit error rate (BER) (namely, BER floor) due to intersymbol interference in frequency-selective Nakagami-Rice fading environments has been developed. The scheme, which we call the equivalent transmission-path model, plays a role in connecting wave propagation with digital transmission characteristics in a general manner. Through computer simulations assuming various types of delay profiles, we first identify key parameters of Nakagami-Rice fading dominating principally the occurrence of irreducible errors and we develop a simple method for the calculation of irreducible BER utilizing the nature or the key parameters. Then we examine the accuracy of the scheme for various types of phase-shift keying (PSK) transmission systems. Finally, based on the scheme, we show calculation examples of BER floor characteristics in line-of-sight fading environments.

Formulation of spatial correlation statistics in Nakagami-Rice fading environments

Propagation environments in line-of-sight (LOS) communications, such as mobile-satellite communications and indoor radio communications, can be expressed by a Nakagami-Rice (or Rician) fading model. Since the Nakagami-Rice fading model also covers the Rayleigh fading model as an extreme case, it seems a very widely applicable model. This paper gives a theoretical formulation of spatial correlation characteristics in the Nakagami-Rice fading environment. Based on this theoretical model, spatial correlation characteristics of Nakagami-Rice fading are clarified comparing with those of Rayleigh fading. Moreover, the difference in spatial correlation characteristics between wide-band signals and narrow-band signals is discussed.

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.

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.

Path loss measurement in 5 GHz macro cellular systems and consideration of extending existing path loss prediction methods

We measured path loss in a macro cellular environment in 5 GHz band. In this paper, existing propagation models for path loss prediction in UHF band are applied to 5 GHz band, and the estimates are compared with the measured data. From the results of the comparison, we describe the differences between the measured and the estimated data.

A Scheme of Secret Key Agreement Based on Received Signal Strength Variation by Antenna Switching in Land Mobile Radio

Schemes for secret key agreement based on the radio transmission path characteristics between authorized stations have been proposed as anti-eavesdropping measures in land mobile radio. In this paper, we propose a new scheme for secret key agreement. It compares the strengths of the signals received at two antennas to produce a bit of the keys. It does not use a threshold which is used in the conventional schemes. We evaluate the performance of the proposed scheme by computer simulation.