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GNSS Signals and Range Determination
Published in Basudeb Bhatta, Global Navigation Satellite Systems, 2021
In FDMA, specific frequencies are allocated to transmitters in order to be identified by the receiver; whereas, in TDMA, individual time slots allow identification; and in CDMA, different codes are assigned to each transmitter (Bellavista and Corradi 2007). Some systems also use a combination of these. The main advantage of CDMA is that the whole bandwidth allocated can be used by every receiver. GPS, Galileo, and BeiDou systems use CDMA, but GLONASS uses FDMA. However, GLONASS is being transformed from FDMA to CDMA. This switchover started in 2014 (with the launch of a GLONASS-M satellite) and is expected to be completed by 2040. Russia has a plan to launch the first GLONASS-K2 satellite by the year 2022. The GLONASS-K2 satellite will allow Russia to evaluate CDMA signals that are planned to broadcast on L1, L2, and L3 frequencies. However, GLONASS will also continue transmitting FDMA signals for the ‘unlimited future’ to provide backward capability.
A Transient Analysis-Based Approach
Published in Mohamed Ibnkahla, Adaptation and Cross Layer Design in Wireless Networks, 2018
CDMA has emerged as the preferred radio transmission technology for the next-generation cellular wireless networks. Resource allocation (i.e., power and transmission rate allocation) in CDMA networks is a crucial problem and needs to be carefully designed to maximize network capacity. Also, admission control is necessary to ensure that the system is not overloaded due to the acceptance of too many calls, and that the QoS requirements of ongoing and accepting calls can be guaranteed. Radio resource allocation and admission control problems in CDMA cellular networks were studied extensively in the literature [3–11]. These problems were also addressed in [12–16] considering multiservice scenarios and different QoS requirements for different types of services. In addition, the optimal resource allocation problem in an integrated CDMA cellular network and wireless LAN (WLAN) was addressed in [17].
Mobile Wireless Technologies
Published in Stephan S. Jones, Ronald J. Kovac, Frank M. Groom, Introduction to COMMUNICATIONS TECHNOLOGIES, 2015
Stephan S. Jones, Ronald J. Kovac, Frank M. Groom
CDMA has been analogized in the following scenario: Within a room filled with people, only two people speak the same language. Each pair of conversationalists needs to be able to talk to each other above the chatter caused by conversations in different tongues. If everyone else in the room maintains the same volume level, conversation between the two parties is possible, and all other conversation sounds like noise to them. In CDMA, the base station of the cellular network defines a specific code in which to encrypt the signal to a mobile phone. The signal is then sent out within a 1.25 MHz bandwidth along with coded information from other conversations. The other conversations, although within the same frequency band as our define call, are detected as noise by the receiving party and rejected. A good definition for CDMA is that it is a technique in which users engage the same time and frequency segment, and are channelized by unique assigned codes. The signals are divided at the receiver by using a correlator that accepts only signal energy from the desired channel. Undesired signals contribute only to noise.
Non-ionizing radiation as possible carcinogen
Published in International Journal of Environmental Health Research, 2022
Shiwangi Gupta, Radhey Shyam Sharma, Rajeev Singh
Several research groups are also working on different wireless technology and its effect on human health. Code division multiple access (CDMA) is a communication method used by different radio technologies that allow multi users to share same frequency band. The transmission power of CDMA is limited to a maximum of 6–7milliWatts (Garg 2000). In early 1990s, 2 G was developed for digital mobile communication systems (GSM or Global System for Mobile Communication). The transmission power intensity of mobile phone is 2 watts in GSM850/900 and 1 watt in GSM1800/1900 (ICNIRP 2009). The third generation (3 G) mobile network technology used to access the internet and the fourth generation (4 G) technology offers high-speed internet access, videos and higher data rates. 5 G or fifth generation of mobile technology provides complete wireless communication with no limitations and 5 G has high speed of transmission rate (Prabhakara et al. 2017). Different specifications of 3 G, GSM and CDMA mobile phone technologies have been shown in Table 4. In connection to the above, Wi-fi can also create a small wireless computer system in a place where they are often called wireless local area networks (WLANs).
Comparative analysis of quaternion modulation system with OFDM systems
Published in International Journal of Electronics Letters, 2021
Anam Zahra, Qasim Umar Khan, Shahzad Amin Sheikh
Every communication system tries to achieve a lower bit error rate (BER) ensuring minimum data loss. With the increasing use of wireless communication technology, the demand for improved BER services over both wired and wireless links is also increased. New techniques are required to transfer data with better BER which existing techniques cannot support (Saxena & Prasad, 2003; Zou & Wu, 1995). In communication system, BER can be achieved at a certain limit at the expense of bandwidth or PAPR (Gangwar & Bhardwaj, 2012). There are various applications to achieve lower BER is more essential as compared to bandwidth such as military communication, point-to-point communication and point-to-multipoint communication (Gallagher, 1979). In the past, various techniques have been implemented in military communication systems to provide protection against noise interference. Spread spectrum is a modulation technique, extensively used in military (Zou & Wu, 1995). It resists interference and makes it hard for enemies to intercept, whereas in spread spectrum modulation technique, the bandwidth of transmitted signal is much greater than the bandwidth of original message. One technique to improve BER is CDMA; it has been used in military applications (Gangwar & Bhardwaj, 2012; Saxena & Prasad, 2003). CDMA is a multiple access technique used with spread spectrum, which allows numerous signals to occupy a single transmission channel in 2G and 3G wireless communications.
Measurement, Analysis, and Understanding of the Error Vector Magnitude (EVM) of Navigation Signals
Published in IETE Journal of Research, 2018
Md. Tosicul Wara, Raghavendra M. R., Kodandaram M., Bhuvaneshwari M. S.
The navigation data (of lower bit rate) is first multiplied with the high speed CDMA code and the multiplied data is then modulated onto the high frequency radio frequency (RF) carrier. The multiplication of data with high speed CDMA code results in spreading of the spectrum and thereby provides the better performance (against noise/jamming, interference, and multipath fading) and better security to the service. For a given navigation satellite, the navigation data, the CDMA code, and the RF carrier all are synchronized in phase. Also, all the satellites in the constellation are synchronized.