Land-mobile communications systems have long been assumed to be reliable, especially by the growing number of radio users in common frequency bands, including ultrahigh frequencies (UHF) and very high frequencies (VHF). Network engineers are usually concerned with a number of different parameters, among them useful radio range, network capacity for radio traffic, and multiple access to channels. But performance parameters typically treated by military users, like protection against radio reconnaissance and interruption/jamming, are rarely analyzed for commercial and civilian radio networks, although such concerns should be addressed by standard Homeland Security defensive measures. Through some straightforward analysis, it should be possible to determine if a radio system designed for reliable communications can also be resistant to reconnaissance and interference.

In Europe, very little in the way of open publications is available on this topic prior to 1990. Up until that time, the majority of problems concerning reconnaissance and counter-reconnaissance efforts were published in the Russian technical literature, translated in part into Polish.^1-5 More detailed scientific descriptions of much of this work were also made available in Polish literature.^6,7 English-language scientific descriptions of reconnaissance and radio countermeasures are not available in Poland, although some of the methodology is available in the literature.^1,3,4,6

Reconnaissance on radio signals should accomplish several things: detecting the operating radio station; determining the signal structure of the transmissions; and determining the information carried in the transmitted signals. This article is concerned with the problems inherent to detecting UHF radio stations and signals. This analysis will build upon a mathematical method for deducing radio signals by the use of the radio reconnaissance equation (R_RE). By applying the R_RE, engineers can determine the energetic secretiveness of various radio transmissions.

To understand radio systems operating with disturbances, it is useful to first analyze such systems without disturbances, using several components in the analysis: transmitter, T, intended radio network receiver, R_U, and reconnaissance receiver, R_R. The analysis involves an investigation of signal power transmitted between transmitter T and receivers R_U and R_R without disturbances. Under these conditions, the received signal power, P_U, at the input of receiver R_U can be defined as:

where:

P_T = the transmit mean power at the transmitter output;
G_TU = the transmit antenna gain;
G_U = the receive antenna gain; and
L_TU = the path loss between transmitter T and receiver R_U.

The received reconnaissance power can be defined as:

where:

G_TU = the transmit antenna gain;
G_R = the reconnaissance receive antenna gain; and
L_TR = the path loss between transmitter T and receiver R_R.

In practice, noise from external sources dominates noise from internal sources in a communications system. The first section of a receiver portion in such a system, referred to as the main receiver path, can be characterized by the usable frequency, F_U, the detection bandwidth, B_O, and the internal noise coefficient, F_I. Once a receiver has processed useful signals, useful signals of average power, P_U or P_R, as well as energy from external noise, appear at the output of the receiver for further processing. In a frequency range from 300 kHz to 300 MHz, the typical median coefficient value for external noise, F_E, for miscellaneous environments, can be estimated by Eq. 3:

F_E = K – 28logf          (3)

where:

K = a special coefficient and
f = the frequency (in MHz).

For coefficient K, mean value amounts for different regions that can be used in this equation include 54 dB for an uninhabited region, 67 dB for a countryside, 72 dB for a suburban area, and 77 dB for a populated, urban area.

The fidelity before detection, r, can defined by Eq. 4 as:

where:

P = the received mean power;
P_N = the mean noise power;
F = the noise coefficient;
F_I = the internal noise coefficient;
F_E = the external noise coefficient;
k = Boltzman’s constant;
B_O = the bandwidth before detection; and
T = the equivalent noise temperature.

The fidelity before detection for receiver R_U , r_U, can be defined by Eq. 5:

where:

P_U = the receiving mean power at the input of receiver R_U;
P_NU = the mean noise power of receiver R_U;
F_IU = the internal noise coefficient of receiver R_U;
F_EU = the external noise coefficient of receiver R_U;
B_OU = the bandwidth before detection of receiver R_U; and
T_U = the equivalent noise temperature of receiver R_U.

The fidelity before detection of receiver R_R , r_R, can be defined by Eq. 6:

where:

P_R = the mean power at the input port of receiver R_R;
P_NR = the mean noise power at the input of receiver R_R;
F_IR = the internal noise coefficient of receiver R_R;
F_ER = the external noise coefficient of receiver R_R;
B_OR = the bandwidth before detection of receiver R_R; and
T_R = the equivalent noise temperature of receiver R_R.

If in Eqs. 5 and 6 the received signal power is replaced by the computed values in Eqs. 1 and 2, the fidelity before detection for the intended network receiver and for the reconnaissance receiver can be found by Eqs. 7 and 8, respectively:

for the network receiver

for the reconnaissance receiver.

In Eqs. 7 and 8, the transmit power can be calculated by applying Eqs. 9-11:

The dependence shown in Eq. 11 is also known as the radio reconnaissance equation (RRE).

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