CDMA is a multiple access technique to allow multiple users to share the same ba

Question

CDMA is a multiple access technique to allow multiple users to share the same bandwidth, based on the orthogonality of their spreading codes. CDMA is a descendent of the direct sequence spread spectrum (DSSS) technology designed for antijam (AJ) and low probability of intercept (LPI) military systems. The spreading gain against jamming or detection is directly related to the ratio of the baseband signal to the spread signal bandwidth, so a spreading factor of 1000 can produce a 30 dB signal processing gain at a receiver that knows the spreading sequece. Frequency hopping is another military technology that can provide high levels of AJ protection. Rather than spreading the signal across all frequencies simultaneously, frequency hopping leaves the original signal bandwidth intact, but jumps from one operating frequency to another, hopefully faster than the jammer is capable of following. Contrast CDMA techniques with frequency hopping and conventional, single frequency systems from the perspective of transmitter and receiver design considerations

Explanation / Answer

Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandomsequence known to both transmitter and receiver. It is used as a multiple access methodin the frequency-hopping code division multiple access (FH-CDMA) scheme.

Spread-spectrum signals are highly resistant to deliberate jamming, unless the adversary has knowledge of the spreading characteristics. Military radios use cryptographic techniques to generate the channel sequence under the control of a secretTransmission Security Key (TRANSEC) that the sender and receiver share in advance.

Conventional single frequency:

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-EIA-95.

It is a 2G mobile telecommunications standard that uses CDMA, a multiple access scheme for digital radio, to send voice, data and signaling data (such as a dialed telephone number) between mobile telephones and cell sites.

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.