Spread spectrum refers to a modulation technique in telecommunications and radio communication where the transmitted signal is spread over a wider frequency band than the minimum necessary for communication. This propagation is carried out using a pseudorandom sequence called a gap code, which modulates the data signal before transmission. The main goals of propagation spectrum are to increase resistance to interference, improve signal security, and improve robustness in harsh communication environments. Propagation spectrum techniques include frequency hopping propagation spectrum (FHSS), direct sequence propagation spectrum (DSS) and others like CHIRP propagation spectrum (CSS) and frequency hopping propagation spectrum. time (THSS), each offering unique benefits based on specific application requirements.
CDMA, or code division multiple access, is called spread spectrum because it uses direct broadcast spectrum (DSSS) techniques. In CDMA systems, each user is assigned a unique deviation code that broadcasts the transmitted signal across the entire available bandwidth. Unlike traditional frequency division multiple access (FDMA) or multiple access systems (TDMA), where users are allocated separate frequency channels or time slots, CDMA allows multiple users to simultaneously share the same frequency band. This propagation of signals across a wide bandwidth allows CDMA systems to achieve higher capacity, improved spectral efficiency, and better resistance to interference compared to other access methods.
Frequency hopping gap spectrum (FHSS) and direct sequence gap spectrum (DSSS) are two main types of gap spectrum techniques:
- FHSS: In FHSS, the transmitter quickly jumps between different frequencies in a predefined sequence. This hopping sequence is synchronized between the transmitter and receiver, allowing data to be transmitted over multiple frequency channels. FHSS is robust against narrow-band interference and provides improved security and reliability in dynamic frequency environments.
- DSSS: DSSS modulates the data signal with a gap code that spreads the signal bandwidth over a much wider frequency range than the original signal bandwidth. This deviation code is a pseudorandom sequence known to both the transmitter and receiver, allowing the receiver to override the signal and recover the original data. DSSS provides increased resistance to interference, improved data integrity, and increased robustness against channel deficiencies such as multipath propagation.
To measure the propagation spectrum, various measurements can be used depending on the specific technique and application. In general, measurements may include evaluation of the bandwidth occupied by the propagation signal relative to the original signal, analysis of the spectral characteristics of the transmitted signal, and evaluation of parameters such as signal-to-noise ratio (SNR), interference levels and signal resistance. Specialized equipment such as spectrum analyzers and signal processing tools are commonly used to measure and analyze propagation spectrum signals in telecommunications, radar systems and other applications.
Whether to disable the propagation spectrum depends on the context and the specific requirements of the application or system. In many cases, propagation spectrum techniques are used to improve signal reliability, improve data security, and mitigate interference effects. Disabling Gap Spectrum may reduce the system’s ability to cope with noise and interference, potentially compromising communication quality or security, particularly in environments prone to electromagnetic interference (EMI). However, in certain specialized scenarios or regulatory environments, a deactivation propagation spectrum may be necessary or mandated. It is important to consider specific operational requirements, performance objectives, and regulatory compliance when deciding whether to enable or disable propagation spectrum in a particular application or system configuration.