Discussion

1. A
PRESANTATION ON DSSS
BY
S/NO STUDENT NAME STUDENT NUMBER
1 ABAHO REGAN KASHOMA 2001201025
2 BLACK SAFI 2001200550
3 ANIKU WILFRED 2001201030
4 TALEMWA ERIA 2001200053
5 AMODING KOLASTIKA 2001200055
6 SSENJOVU EMMANUEL JOSTER 2001200052

2. DIRECT SQUENCE SPREAD
SPECTRUM(DSSS)
 Direct sequence spread spectrum (DSSS) is a transmission technology
used in local area wireless network transmissions. In this technology, a
data signal at the sending station is combined with a high data rate bit
sequence, which divides user data based on a spreading ratio.
 This term is also known as direct sequence code division multiple access
 It was originally developed for military use, and employed difficult-to-detect
wideband signals to resist jamming attempts.
 It is also being developed for commercial purposes in local and wireless
networks.

3. Explains Direct Sequence Spread
Spectrum (DSSS)
.The stream of information in DSSS is divided into small pieces, each associated with a
frequency channel across spectrums.
 Data signals at transmission points are combined with a higher data rate bit sequence, which
divides data based on a spreading ratio.
 The chipping code in a DSSS is a redundant bit pattern associated with each bit transmitted.
This helps to increase the signal's resistance to interference. If any bits are damaged during
transmission, the original data can be recovered due to the redundancy of transmission.
 The entire process is performed by multiplying a radio frequency carrier and a pseudo-noise
(PN) digital signal.
 The PN code is modulated onto an information signal using several modulation techniques
such as quadrature phase-shift keying (QPSK), binary phase-shift keying (BPSK), etc.

4. Fig 1 shows
(a)Direct sequence spread spectrum (DSSS) system model and (b) DSSS
spreading operation; the pseudo noise (PN) sequence in this example is 00010

5. DSSS Demodulator.
 The DSSS demodulator applies the correlation operation in two processing phases:
acquisition in synchronization establishment stage, and decoding in data
 DSSS demodulator - This block implements a sliding correlator, combining the two
correlation processes in the synchronization and data decoding stages.
 The sliding correlator first correlates the received bit stream from the constellation
decoder with chips of the PN sequence to produce a correlation result

6. DSSS Modulator
Acquisition phase
 In the acquisition phase, correlation can be
performed in parallel or sequentially .
 A parallel correlation system consists of a
series of correlators.
 Each correlator corresponds to a phase shifting
version of the PN sequence, apart from each
other with 1/2 of the chip duration in time.
 The incoming signal is fed into this set of
correlators simultaneously.
 A comparator circuit reads correlation results
from these correlators and locates the largest
one.
Synchronization phase
 The shifting version of PN sequence
corresponding to the largest correlation result is
then used to adjust the clock of the PN
sequence generator and the synchronization is
established.
 On the other hand, a sequential correlation
system contains only one correlator, which
correlates the incoming signal with a copy of
the PN sequence and compares the correlation
result to a threshold. If the threshold is
satisfied, the synchronization is considered
successful, otherwise the PN sequence shifts
1/2 of the chip duration, and the correlator
performs the previous operations again, until
the threshold is satisfied.

7. Implementation of a Direct Sequence
Spread Spectrum
Baseband Transmitter
 it is used in several areas including cellular
phones, wireless LANs, satellite
communication, and even gas and water meters.
 The capabilities of the digital blocks in the
PSoC software are well suited for many of the
baseband functions required to transmit a
spread spectrum signal, providing a low-cost
and highly integrated solution with many
additional features.
NOTE: Spread spectrum can also
be implemented by a
combination of the two.
Spread Spectrum Primer
 Spread spectrum RF transmission involves
spreading out the power spectrum of an RF
signal using a code.
 The same code is then used to receive the
signal. This has tremendous benefits, including
shared bandwidth between multiple users using
multiple codes, reduction of interference
experienced by other users of the spectrum, and
resistance to external interference, jamming,
multipath effects, and eavesdropping. Spread
spectrum usually involves changing the
transmission frequency of a signal over time
(frequency hopping) or combining a signal with
a Pseudo-random Noise (PN) code before
transmission (direct sequence or DS).

8. Direct sequence spread spectrum
applications
 Covert communications: DSSS was first used to provide secure and covert
communications. The signals were initially difficult to detect as they sounded like
broadband noise and often would have been mistaken for that. Also, to access the data it is
necessary to know the code used to generate the signal
 Code Division Multiple Access(CDMA) cellphone technology: The DSSS technique was
used to provide a multiple access scheme that was used for 3G cellophane technology. Each
mobile used a different access code or spreading code and this enabled multiple users to
access the base station on the same frequency.
 Global Navigation Satellite System(GNS): : Satellite based navigation systems use
DSSS as this gives a signal gain by spreading the signal out over a wide bandwidth. It also
enables different satellites to use the same channel without mutual interference.

9. BENEFITS OF DSSS.
 Resistance to unintended or intended jamming
 Sharing of a single channel among multiple users
 Reduced signal/background-noise level hampers interception.
 Determination of relative timing between transmitter and receiver.

10. REFFERENCES
[1] C. J. Biermann. Handbook of pulping and papermaking. Academic press, 1996.
[2] L. Choong. Multi-channel ieee 802.15. 4 packet capture using software defined radio. University of California. http: // nesl. ee. ucla. edu/ fw/
thomas/ leslie_ choong_ multichannel_ ieee802154. pdf , 2009.
[3]. J. S. Lee and L. E. Miller, CDMA Systems Engineering Handbook, Norwood, MA: Artech House Inc., 1998.
[4]. M. Simon, J. Omura, R. Scholtz, and B. Levitt, Spread Spectrum Communications Handbook, New York, NY: McGrawHill, 1994.
[5]. Institute of Electrical and Electronics Engineers (IEEE), “IEEE Standards for local and metropolitan area networks, part 11: wireless LAN
medium access control (MAC) and physical layer (PHY) specifications,” IEEE Standard 802.11- 1997, 1997.
[6]. Institute of Electrical and Electronics Engineers (IEEE), “IEEE Standard for information technology: local and metropolitan area networks,
specific requirement, part 15.4: wireless medium access control (MAC) and physical layer (PHY) specifications for low rate wireless personal area
networks (WPANs),” IEEE Standard 802.15.4-2006, 2006.
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