Shigeru Kozono

Mobile propagation loss and delay spread characteristics with a low base station antenna on an urban road

Propagation loss and delay spread were studied experimentally, in order to design digital mobile communication systems. For propagation loss, the results were as follows, (i) When there are no obstacles on the road, the distance over which a radio wave propagates with only free-space loss increases with frequency. (ii) When there are obstacles (trucks and buses). and when the base station antenna heights are 5 and 15 m. the loss in excess of the free-space loss is 15 and 10 dB, respectively, at 1 km, (iii) Frequency dependence of this excess loss is not significant. (iv) On a cross road. the loss increases rapidly traveling away from the intersection. For the delay spread. the results were as follows. (i) The delay spread increases slightly with distance (less than 0.3 mu s within 1 km). (ii) The standard deviation of the delay spread increases slightly with distance (less than 0.2 mu s). Using the above results. a service area that extends along the road on which the base station is located and is limited in distance along cross roads can be predicted. >

Received signal-level characteristics in a wide-band mobile radio channel

A mobile propagation model aimed at clarifying fundamental propagation characteristics in received signal-level variation for wide-band transmission is proposed. On the basis of this model, the author derives an expression for a received signal level in wide-band transmission and examines the fundamental signal-level characteristics by computer simulation and experiment. Both simulation and measurement results agree well and the results follow. For a received signal-level variation in wide-band transmission: first, received signal-level depth becomes shallower with increasing receiver bandwidth 2/spl Delta/f, and the level has no Rayleigh distribution. In an urban area when 2/spl Delta/f is 3 MHz, the level difference between the cumulative probability 50% and 1% values is about 5 dB. Second, received signal-level distribution depends on the number of arriving waves N and path length difference |/spl Delta/L/sub ij/|. The level depth becomes shallower with increasing N and |/spl Delta/L/sub ij/|. Third, received signal-level distribution is almost independent of radio frequency f/sub c/. The author also derives expressions for the autocorrelation coefficient /spl rho/(z) and frequency coefficient /spl rho/(s) of the received signal level. /spl rho/(z) is independent of 2/spl Delta/f, and is about J/sub 0/(Z//spl lambda//sub c/)/sup 2/, which is known as narrow-band reception. The /spl rho/(s) becomes higher with increasing 2/spl Delta/f. >

Co-channel interference measurement method for mobile communication

A new method of measuring co-channel interference for mobile communication systems is proposed. In this method, the carrier envelope is sampled, and signal-carrier-to-interference-carrier ratio (CIR) is calculated by signal processing. The circuits for measurement are composed of an envelope detector, an analog-to-digital converter, and a microcomputer. Theoretical and experimental evaluations of measurement errors are examined, and the method is proved to be promising. Using this method, the signal-to-interference ratio of up to 20 dB is measured, within 2 dB error for fading frequency of less than 80 Hz.

A study of received signal-level distribution in wideband transmissions in mobile communications

A mobile propagation model, which includes not only indirect arriving waves but also a direct arriving waves and is applicable to picocell, microcell, and macrocell, is proposed in order to clarify fundamental propagation characteristics in instantaneous received signal-level variation through narrowband and wideband transmissions. On the basis of this model, we derive a mathematical expression for the instantaneous received signal-level. Through an analysis of this expression, a new propagation parameter called equivalent received bandwidth 2/spl Delta/f/spl Delta/L/sub max/ is proposed. The dependence of the received signal-level distribution on the new parameter is studied by computer simulation. It is shown that the fading depth depends strongly on the 2/spl Delta/f/spl Delta/L/sub max/, as a parameter of the power ratio a. When 2/spl Delta/f/spl Delta/L/sub max/ 10 MHz/spl middot/m, the fading depth depends not only on the power ratio a but also on the 2/spl Delta/f/spl Delta/L/sub max/ and it decreases as 2/spl Delta/f/spl Delta/L/sub max/ increases. On the other hand, the number of arriving waves and the minimum effective amplitude of arriving waves are examined quantitatively. According to the results, when the number of arriving waves N is larger than 6, the fading depth is independent of N, and the minimum amplitude of arriving waves should be larger than -20 dB relative to the maximum amplitude in indirect arriving waves.

Theoretical analysis of frequency-correlation coefficient for received signal level in mobile communications

Frequency-correlation coefficient characteristics that define frequency separation in frequency-diversity techniques were studied theoretically using a propagation model that makes allowances for received bandwidth. Equations of frequency-correlation coefficients in non- and line-of-sight propagation paths were derived. The equations showed that frequency-correlation coefficient depends on such factors as frequency separation, received bandwidth, differences in pathlengths, and the power ratios of the direct to indirect waves. The frequency-correlation coefficient increases as the received bandwidth increases and decreases as the difference in pathlength increases. However, when the difference in the pathlength was small (30 m), the effect of the received bandwidth was minimal. The frequency-correlation coefficient also depended somewhat on the power ratio. To confirm the accuracy of our theoretical derivations, computer simulations were performed. Frequency-correlation coefficients were calculated by simulating instantaneous received signal levels. The theoretical results matched those of the simulation.

MIMO Channel Model with Propagation Mechanism and the Properties of Correlation and Eigenvalue in Mobile Environments

This paper described a spatial correlation and eigenvalue in a multiple-input multiple-output (MIMO) channel. A MIMO channel model with a multipath propagation mechanism was proposed and showed the channel matrix. The spatial correlation coefficient formula 𝜌𝑖−𝑗,𝑖′−𝑗′(𝑏𝑚) between MIMO channel matrix elements was derived for the model and was expressed as a directive wave term added to the product of mobile site correlation 𝜌𝑖−𝑖′(𝑚) and base site correlation 𝜌𝑗−𝑗′(𝑏) without LOS path, which are calculated independently of each other. By using 𝜌𝑖−𝑗,𝑖′−𝑗′(𝑏𝑚), it is possible to create the channel matrix element with a fixed correlation value estimated by 𝜌𝑖−𝑗,𝑖′−𝑗′(𝑏𝑚) for a given multipath condition and a given antenna configuration. Furthermore, the correlation and the channel matrix eigenvalue were simulated, and the simulated and theoretical correlation values agreed well. The simulated eigenvalue showed that the average of the first eigenvalue λ1 hardly depends on the correlation 𝜌𝑖−𝑗,𝑖′−𝑗′(𝑏𝑚), but the others do depend on 𝜌𝑖−𝑗,𝑖′−𝑗′(𝑏𝑚) and approach 𝜆1 as 𝜌𝑖−𝑗,𝑖′−𝑗′(𝑏𝑚) decreases. Moreover, as the path moves into LOS, the 𝜆1 state with mobile movement becomes more stable than the 𝜆1 of NLOS path.

Study of Correlation Coefficients of Complex Envelope and Phase in a Domain with Time and Frequency Axes in Narrowband Multipath Channel

As a basic multipath property required to allocate the pilot signal in orthogonal frequency division multiplexing (OFDM) and compose antennas in the multiple-input multiple-output (MIMO) technique, correlation coefficients of the complex envelope in the received signal level and phase in multipath channels were studied theoretically and by computer simulation in a domain with time, frequency, and space axes. First, correlation coefficient rho e (Deltax) of the envelope was derived in the domain with a variable Deltax= f m T s + Deltafsigma, where f m T s is on the time axis (f m T s : normalized maximum fading frequency) and Deltafsigma is on the frequency and space axes (Af. frequency separation, sigma: delay spread). Birds-eye views of rho e (Deltax) and rho p (Deltax) of the phase in multipath channels are shown in the domains to give a good overall grasp of them. The theoretical values of rho e (Deltax) and rho p (Deltax) agree with the simulated ones. Furthermore, it is shown that the cumulative distributions influenced on bit error rate performance depended strongly on Deltax and spread as Deltax increased.

A Study of Narrow Band Multi-path Channel Phase Difference Characteristics on Domain with Time and Frequency Axes

Multi-path phase difference distribution in a narrow mobile radio channel, which is required for allocating a pilot signal and predicting bit error rate (BER) degradation, was studied on a domain with time f_mT_s and frequency f₀sigma axes using theoretical and simulated results. Assuming that multi-path amplitude decreases exponentially, and multi-path phase thetas(t, f_c), symbol period of digital signal T_s, sub-channel bandwidth f₀, the total phase difference zeta;zeta = thetas(t+T_s, f_c+f₀) - thetas(t, f_c) was discussed in great detail by using the cumulative distribution. First, we verified that the theoretical cumulative distribution obtained by (4) and (6) showed good agreement with the simulated distribution with a wide range of 0.001 to 99.999 %. Next, a phase difference cumulative value locus was determined by using coordinates (f_mT_s, f₀sigma) on a domain with time and frequency axes for a certain cumulative value. Last, for the phase difference applications, we showed that using the cumulative value enabled the M-array differential quadrature phase shift keying BER to be estimated and using the locus enabled a pilot signal on the domain to be allocated flexibly.

A method for expressing mobile propagation loss characteristics in a street microcell system

Data from the received signal-level in the personal handy-phone system commercial communication service are used to evaluate a method for expressing mobile propagation loss characteristics. The standard deviation of the difference between the measured signal level and the signal level given by empirical equations is calculated on the basis of a macrocell mode (loss versus direct distance from base station) and a street microcell mode (classified as base-station road and crossed road). The results show that the expression of street microcell mode is better than that of the macrocell mode.

Correlation Coefficients of Received Signal I and Q Components in a Domain with Time and Frequency Axes under Multipath Mobile Channel with LOS and NLOS

To support realtime multimedia communication, future mobile communications will require a high-bit-rate transmission system with high utilization of the frequency spectrum in very rich multipath channels [1]. Systems capable of fulfilling this requirement, with features such as orthogonal frequency division multiplexing (OFDM) [2], [3] and multiple-input multiple-output (MIMO) [4]–[7], have been studied extensively. Furthermore, the use of Mary quadrature amplitude modulation (M-ary QAM) with coherent detection helps to meet the transmission requirements. Such systems overcome frequency selective fading by using a narrowband multiple-carrier signal called a sub-channel. Those systems use sophisticated and refined techniques and several of those techniques are usually combined in one system. To make full use of the techniques in the system design and achieve high-quality transmission, we must design a system taking into consideration wide and detailed multipath properties in a domain with time and frequency axes. OFDM works best with a lot of narrow bands for the sub-channel. MIMO also requires multipath properties between the antennas composing the MIMO antenna, and it requires a low correlation coefficient. Mary QAM detection also requires the device to compensate accurately for both the in-phase and quadrature (I and Q) components of the sub-channel for the ever-changing multipath channel associated with terminal movement, and this is achieved by putting a pilot signal in the information data [8]. Figure 1 shows an example of the sub-channel state of the I and Q components and phase ψ (tan-1(Q/I)) as movement in a multipath channel, and Fig. 2 shows the signal state diagram at the moment. With movement, the I, Q, and the phase ψ change irregularly as shown by solid lines in Fig.1, so we cannot use the sub-channel as a transmission line. Therefore, the subchannel needs to be a stable state with compensation by a pilot signal. The states of the subchannel compensated every 10Tsy (Tsy: symbol length) in information data, which