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IS 95 CDMA
IS 95 CDMA
IS 95 CDMA 
IS‐95 CDMA
• The existing 12.5 MHz cellular bands are used to derive 10
g
different CDMA bands (1.25 MHz per b...
• Interim Standard 95 (IS-95) is the first CDMA-based
(
)
digital cellular standard by Qualcomm. The brand name
for IS-95 ...
• CDMA permits several radios to share the same
frequencies.
frequencies
• Unlike TDMA "time division multiple access", a
...
Protocol details
Protocol details
• The IS-95 standards describe an air interface, a set of
protocols used between mobile ...
Physical layer
Physical layer
• IS-95 defines the transmission of signals in both the forward
g
f
(network-to-mobile) and ...
The Logical Channels
Pilot channel
Paging channels
Forward
channels

Variable-bit-rate
user information

Sync channels
Pow...
IS 95
IS-95 CDMA Forward Channel
• The forward link uses the same frequency spectrum as AMPS
q
y p
(824-849 Mhz)
• Each ca...
IS 95
IS-95 CDMA Reverse Channel
•
•
•
•
•
•
•

Fundamentally different from the forward channels
y
Uses OQPSK for power e...
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6. is 95

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Transcript of "6. is 95"

  1. 1. IS 95 CDMA IS 95 CDMA
  2. 2. IS 95 CDMA  IS‐95 CDMA • The existing 12.5 MHz cellular bands are used to derive 10 g different CDMA bands (1.25 MHz per band). • The frequency reuse factor in CDMA is 1. • The channel rate is 1.2288 Mbps (actually chips not bits) • Multipath fading is exploited in CDMA. It provides for space (path) diversity diversity. • RAKE receivers are used to combine the output of several received signals.
  3. 3. • Interim Standard 95 (IS-95) is the first CDMA-based ( ) digital cellular standard by Qualcomm. The brand name for IS-95 is cdmaOne. IS-95 is also known as TIA-EIA95. 95 • It is a 2G mobile telecommunications standard that uses CDMA, a multiple access scheme for digital radio, to send voice, d d i data and signaling d d i li data ( h as a di l d (such dialed telephone number) between mobile telephones and cell sites. • CDMA or "code division multiple access" is a digital radio system that transmits streams of bits (PN codes).
  4. 4. • CDMA permits several radios to share the same frequencies. frequencies • Unlike TDMA "time division multiple access", a competing system used in 2G GSM all radios can be GSM, active all the time, because network capacity does not directly limit the number of active radios. y • Since larger numbers of phones can be served by smaller numbers of cell-sites, CDMA-based standards have a significant economic advantage over TDMAbased standards, or the oldest cellular standards that used f d frequency-division multiplexing. di i i li l i
  5. 5. Protocol details Protocol details • The IS-95 standards describe an air interface, a set of protocols used between mobile units and the network network. • IS-95 is widely described as a three-layer stack, where • L1 corresponds to the physical (PHY) layer, ( ) • L2 refers to the Media Access Control (MAC) and LinkAccess Control (LAC) sublayers, and • L3 to the call-processing state machine.
  6. 6. Physical layer Physical layer • IS-95 defines the transmission of signals in both the forward g f (network-to-mobile) and reverse (mobile-to-network) directions. • In the forward direction, radio signals are transmitted by base stations (BTS' ) t ti (BTS's). • Every BTS is synchronized with a GPS receiver so transmissions a e t g t y co t o ed are tightly controlled in time. All forward transmissions are t e. o wa d t a s ss o s a e QPSK with a chip rate of 1.2288 Mbps.
  7. 7. The Logical Channels Pilot channel Paging channels Forward channels Variable-bit-rate user information Sync channels Power control Traffic channels Logical channels Signaling messages Access channels Reverse channels Variable-bit-rate user information Traffic h T ffi channels l Signaling messages 7
  8. 8. IS 95 IS-95 CDMA Forward Channel • The forward link uses the same frequency spectrum as AMPS q y p (824-849 Mhz) • Each carrier 1.25MHz • 4 types of logical channel: A pilot, a synchronization, 7 paging, and 55 traffic channels • Channels are separated using different spreading codes • QPSK is the modulation scheme • Orthogonal Walsh codes are used (64 total) g ( ) • After orthogonal codes, they are further spread by short PN spreading codes • Short PN spreading codes are M sequences generated by LFSRs of length 15 with a period of 32768 chips.
  9. 9. IS 95 IS-95 CDMA Reverse Channel • • • • • • • Fundamentally different from the forward channels y Uses OQPSK for power efficiency QPSK demodulation is easy 869-894 MHz range No spreading of the data using orthogonal codes Same orthogonal codes are used for WAVEFORM encoding Two types of logical channels: The access channels and the reverse traffic channels
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