Flexible - Read on multiple operating systems and devices. Easily read eBooks on smart phones, computers, or any eBook readers, including Kindle. We cannot process tax exempt orders online. If you wish to place a tax exempt order please contact us. Add to cart. Sales tax will be calculated at check-out. Free Global Shipping. Description Most books in wireless communications address technical subjects which are relevant to ground mobile systems. Free Global Shipping. Description Volume One of the Wireless Communications Design Handbook provides an in-depth look at interference problems in satellite communications.
The material presented is from a satellite or spacecraft hardware point of view rather than from theoretical models. Each satellite subsystem is described in detail to point out interference and noise problems associated with it.
The book also addresses typical architectures and hardware design issues in satellites. In addition, a detailed look at space interference is discussed with emphasis on the possible impact on satellite electronics. An applications-oriented reference for engineers, system designers, and practitioners Addresses the most common interference concerns in ground mobile wireless communications systems Hardware-oriented approach to interference and noise concerns as well as satellite subsystem design All satellite subsystems described in great technical detail Significantly covers space interference with a slanted approach to satellite hardware effects Covers modern hardware design for low earth orbit satellites to be used in wireless communications.
Engineers, practitioners in the field, graduate courses in wireless communications in electrical engineering and computer science. However, the technique that is used is a timeout.
If the source does not receive an acknowledgment to data within a given period of time, the source retransmits. The header in TCP is of variable length. In practice, there will be some beam spread.
Nevertheless, it produces a highly focused, directional beam. Intermodulation noise produces signals at a frequency that is the sum or difference of the two original frequencies or multiples of those frequencies. Crosstalk is the unwanted coupling between signal paths. Impulse noise is noncontinuous, consisting of irregular pulses or noise spikes of short duration and of relatively high amplitude.
The edge in effect become a source and waves radiate in different directions from the edge, allowing a beam to bend around an obstacle. If the size of an obstacle is on the order of the wavelength of the signal or less, scattering occurs. An incoming signal is scattered into several weaker outgoing signals in unpredictable directions.
Selective fading affects unequally the different spectral components of a radio signal. With frequency diversity, the signal is spread out over a larger frequency bandwidth or carried on multiple frequency carriers.
Time diversity techniques aim to spread the data out over time so that a noise burst affects fewer bits. Half of that is 5, km which is comparable to the east-to-west dimension of the continental U. While an antenna this size is impractical, the U. Defense Department has considered using large parts of Wisconsin and Michigan to make an antenna many kilometers in diameter.
Using Equation 5. From Table 5. The available received signal power is 20 — This approach is susceptible to sudden gain changes and is rather inefficient. A disadvantage of NRZ transmission is that it is difficult to determine where one bit ends and the next bit begins. For PM, the phase is proportional to the modulating signal.
For FM, the derivative of the phase is proportional to the modulating signal. First consider NRZ-L. For the remaining codes, one must first determine the average number of pulses per bit. For example, for Biphase-M, there is an average of 1. These higher components cause the signal to change more rapidly over time.
Hence, DM will suffer from a high level of slope overload noise. PCM, on the other hand, does not estimate changes in signals, but rather the absolute value of the signal, and is less affected than DM. The demodulator portion of a modem expects to receive a very specific type of waveform e. Thus, it would not function as the coder portion of a codec. The case against using a codec in place of a modem is less easily explained, but the following intuitive argument is offered.
If the decoder portion of a codec is used in place of the modulator portion of a modem, it must accept an arbitrary bit pattern, interpret groups of bits as a sample, and produce an analog output. Some very wide value swings are to be expected, resulting in a strange-looking waveform.
Given the effects of noise and attenuation, the digital output produced at the receiving end by the coder portion of the codec will probably contain many errors. The actual step size, in volts, is: 0. Thus the actual maximum quantized voltage is: 0. The normalized step size is 2—8. The maximum error that can occur is one-half the step size. Only a recipient who knows the spreading code can recover the encoded information.
A receiver, hopping between frequencies in synchronization with the transmitter, picks up the message. Each user uses a different spreading code. The receiver picks out one signal by matching the spreading code. Cross-correlation, which is defined in Equation 7. Thus, to achieve the desired SNR, the signal must be spread so that 56 KHz is carried in very large bandwidths.
Thus a far higher SNR is required without spread spectrum. Source: [SKLA01] 7. MFSK c. Same as for Problem 7. This is from the example 6.
We need three more sets of 8 frequencies. The second set can start at kHz, with 8 frequencies separated by 50 kHz each. The third set can start at kHz, and the fourth set at kHz. The first generator yields the sequence: 1, 6, 10, 8, 9, 2, 12, 7, 3, 5, 4, 11, 1,. The second generator yields the sequence: 1, 7, 10, 5, 9, 11, 12, 6, 3, 8, 4, 2, 1,.
Because of the patterns evident in the second half of the latter sequence, most people would consider it to be less random than the first sequence. See [KNUT98], page 13 for a discussion. As discussed in the answer to Problem 10, this leads to results in which the right-hand digits are much less random than the left-hand digits.
Often, a and c are chosen to create a sequence of alternating even and odd integers. The simulation depends on counting the number of pairs of integers whose greatest common divisor is 1.
With truly random integers, one-fourth of the pairs should consist of two even integers, which of course have a gcd greater than 1. This never occurs with sequences that alternate between even and odd integers. For a further discussion, see Danilowicz, R. That is, it provides more information that can be used to detect errors. You could design a code in which all codewords are at least a distance of 3 from all other codewords, allowing all single-bit errors to be corrected.
Suppose that some but not all codewords in this code are at least a distance of 5 from all other codewords. Then for those particular codewords, but not the others, a double- bit error could be corrected.
The source station receiving the NAK will retransmit the frame in error plus all succeeding frames transmitted in the interim. The modulo 2 scheme is easy to implement in circuitry. It also yields a remainder one bit smaller than binary arithmetic.
Each 1 bit will merge with a 1 bit exclusive-or to produce a 0; each 0 bit will merge with a 0 bit to produce a zero. The HDLC standard provides the following explanation. The addition of XK L X corresponds to a value of all ones.
This addition protects against the obliteration of leading flags, which may be non-detectable if the initial remainder is zero. The addition of L X to R X ensures that the received, error- free message will result in a unique, non-zero remainder at the receiver.
The non-zero remainder protects against the potential non-detectability of the obliteration of trailing flags. The implementation is the same as that shown in Solution 3b, with the following strategy. At both transmitter and receiver, the initial content of the register is preset to all ones. The final remainder, if there are no errors, will be For simplicity, we do not show the switches. The partial results from the long division show up in the shift register, as indicated by the shaded portions of the preceding table.
Compare to long division example in Section 8. Five additional steps are required to produce the result. For a codeword w to be decoded as another codeword w', the received sequence must be at least as close to w' as to w. Therefore all errors involving t or fewer digits are correctable.
Now suppose that the only error is in C8. Thus, the data word read from memory was The minimum value of n — k that satisfies this condition is The first column is filled after 21 bits are read in. Similarly, 21 bits must arrive before deinterleaving. This clears out the encoder, making it ready for use for the next transmission. The sequence of states traversed is abdcbcbdcb. The output sequence is 10 11 10 01 01 01 11 10 01 00 8.
Because only one frame can be sent at a time, and transmission must stop until an acknowledgment is received, there is little effect in increasing the size of the message if the frame size remains the same. All that this would affect is connect and disconnect time. This would lower line efficiency, because the propagation time is unchanged but more acknowledgments would be needed.
For a given message size, increasing the frame size decreases the number of frames. This is the reverse of b. The first frame takes 10 msec to transmit; the last bit of the first frame arrives at B 20 msec after it was transmitted, and therefore 30 msec after the frame transmission began. It will take an additional 20 msec for B's acknowledgment to return to A. Thus, A can transmit 3 frames in 50 msec. B can transmit one frame to C at a time.
The larger the area of coverage, the more satellites must be involved in a single networked system. General usage: commercial, military, amateur, experimental. In the case of a geostationary satellite, a single antenna is visible to about one-fourth of the earth's surface.
Thus, satellite-to-satellite communication links can be designed with great precision. An equatorial orbit is directly above the earth's equator. A polar orbit passes over both poles. Other orbits are referred to as inclined orbits. The traditional GEO satellite is in a circular orbit in an equatorial plane such that the satellite rotates about the earth at the same angular velocity that the earth spins on its axis. LEO satellites are satellites with much lower orbits, on the order of to 1, km high.
Finally, HEO satellites are characterized by an orbit that is an ellipse with one axis very substantially larger than the other. The height of the orbit can vary; it is the shape of the orbit that characterizes this type of satellite. Frequency reuse is more difficult because the antenna beam all other things being equal covers a much greater area from a GEO than from a LEO.
On the other hand, tracking and handoff is not necessary for GEO satellites because they appear stationary relative to the earth. LEO satellites, since they are so low travel very much faster, and cover less area than GEO so that tracking is more difficulty and passing off is frequent. HEOs require tracking and handoffs, as well. HEOs are primarily of use when coverage of areas near one of the poles is essential, such as the use of the Molniya satellites to cover the northern parts of the former Soviet Union.
LEOs are useful for point-to-point communication, and for extensive frequency reuse. Since LEOs have much less propagation delay they are useful for interactive data services. They also can cover polar regions.
The received power will increase by a factor of 4 9. The total available capacity is 60 Mbps. Frequency borrowing: In the simplest case, frequencies are taken from adjacent cells by congested cells. The frequencies can also be assigned to cells dynamically.
Cell splitting: In practice, the distribution of traffic and topographic features is not uniform, and this presents opportunities of capacity increase. Cells in areas of high usage can be split into smaller cells. Cell sectoring: With cell sectoring, a cell is divided into a number of wedge-shaped sectors, each with its own set of channels, typically 3 or 6 sectors per cell.
Each sector is assigned a separate subset of the cell's channels, and directional antennas at the base station are used to focus on each sector. Microcells: As cells become smaller, antennas move from the tops of tall buildings or hills, to the tops of small buildings or the sides of large buildings, and finally to lamp posts, where they form microcells.
Each decrease in cell size is accompanied by a reduction in the radiated power levels from the base stations and the mobile units. Microcells are useful in city streets in congested areas, along highways, and inside large public buildings. In this case, the mobile unit is handed off to a neighboring cell based not on signal quality but on traffic capacity. Call dropping probability: the probability that, due to a handoff, a call is terminated. Call completion probability: the probability that an admitted call is not dropped before it terminates.
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