In the receiver the received signal is XORed with the PN stream to recover the original data stream; this is equivalent to correlation with the known PN sequence. At the intended receiver, despreading is accomplished by cross-correlation of the received spread signal with a synchronized replica of the same code signal used to spread the data. A pseudo-random code is generated, matching the anticipated signal. Nominal deviations of the four levels are ± 72 and ± 216 kHz. The chipping code in a DSSS is a redundant bit pattern associated with each bit transmitted. DSSS technology uses more bandwidth than FHSS, but is considered more reliable and resists interference. This is achievable for local radio systems and transmission lines, but can be much harder to achieve over a wide bandwidth in long distance radio links. For longer intervals, there are many non-conjugate and conjugate CFs for DSSS BPSK. The length field indicates the number of microseconds necessary to transmit the MPDU. An 11-bit Barker code (1, −1, 1, 1, −1, 1, 1, 1, −1, −1, −1) is used for spreading. For DSSS operation, the 2.4-GHz ISM band is divided into three nonoverlapping or six overlapping frequency bands, as shown in Figure 25.9. Modulation types & techniques But instead of a pseudorandom binary sequence (PRBS), an 11-bit Barker code is used as the spreading sequence. Amplitude modulation In Figure 2, the narrowband signal and the spread-spectrum signal both use the same amount of transmit power and carry the same information. In the given example, the spread signal of the user A at the code A, and diffused signal … The result in the frequency domain is a signal that is spread over a wide bandwidth at a reduced RF power level. There is an obvious analogy between this process and stream ciphering (Section 14.8) but with the crucial difference that in DSSS the PN sequence is at a much greater clock frequency than the data stream. ▶︎ Ethernet Products. In direct sequence spread spectrum (DSSS), the transmitter and receiver contain identical psuedo-random sequence generators producing a pseudo-noise (PN) signal. In telecommunications, direct-sequence spread spectrum (DSSS) is a spread-spectrum modulation technique primarily used to reduce overall signal interference. This presents a particular challenge for fast FH systems. DSSS is used in a number of areas where its properties have enabled it to provide some unique advantages over other techniques. With this channel arrangement, a user can configure multiple DSSS networks to operate simultaneously in the same area. With DSSS, the data is divided and simultaneously transmitted on as many frequencies as possible within a particular frequency band (the channel). ▶︎ HDMI Products. Note: Electronics Notes receives a small commission on sales at no cost to you. The signal field indicates which modulation scheme should be used to receive the incoming MPDU. The non-conjugate CFs for DSSS QPSK are identical to those for DSSS BPSK, and the conjugate CFs are not present. Synchronization is achieved in 802.11 by sending the essential parameters—dwell time, frequency sequence number, and present channel number—in a frequency parameter set field that is part of a beacon transmission sent periodically on the channel. The first part of the process is to generate the DSSS signal. This injection is known as the spreading operation. The baseband data stream is then modulated onto a carrier and in this way the overall the overall signal is spread over a much wider bandwidth than if the data had been simply modulated onto the carrier. In DSSS, the PN sequence spreads the spectrum of the signal by the chipping rate, resulting in the instantaneous widening of the spectrum. Direct Sequence Spread Spectrum, DSSS Includes: Three Non-Overlapping DSSS The Direct Sequence Spread Spectrum modulation makes the transmitted signal wider in bandwidth than the information bandwidth. various options of the Wide-Band Direct Sequence Spread Spectrum (WB-DSSS) scheme. In order to visualise how the direct sequence spread spectrum process operates, the easiest method is to show an example of how the system actually operates in terms of data bits, and how the data is recovered from the DSSS, direct sequence spread spectrum signal. Receiver sensitivity must be better than − 80 dBm for a 3% frame error rate. Data bits are grouped into symbols of two bits, so each symbol can have one of four levels. 4. Direct-sequence spread spectrum (DSSS) is one of two types of spread spectrum radio, the other being frequency-hopping spread spectrum.. DSSS Transmission. The information-bearing baseband signal is denoted as v(t) and is expressed as ( ) { 1, }v t a g t nT where a nn T b n( ) n ∞ = − =± −∞< <∞∑ =−∞ and g T (t) is a rectangular pulse of duration T b This signal is multiplied by the signal … 11. Table 6.1 provides a summary of access technologies used for various wireless systems. The physical layer provides three levels of functionality. Table 21.5 lists the DSSS channels used in different parts of the world. Direct-sequence acquisition and tracking A direct-sequence-spread-spectrum receiver must despread the received signal to recover the transmitted data. In the receiver the received signal is XORed with the PN stream to recover the original data stream; this is equivalent to correlation with the known PN … However once received and processed with the correct descrambling codes, it is possible to extract the required data. DSSS direct sequence spread spectrum encode / decode process. On the other hand, FDMA and TDMA radios must be carefully assigned a frequency or time slot to assure that there is no interference with other similar radios. Radio Signals By using this, the transmission signal of each user can be identified by the separate code when it receives the signal. The spreading code spreads the signal across a wider frequency band in … Radio receiver types The maximum allowable radiated power for DSSS PHY varies from region to region (refer to Table 21.6). The SYNC field is 128 bits (symbols) in length and contains a string of 1s which are scrambled prior to transmission.