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Anonymous users2024-02-06CDMA is the abbreviation of Code Division Multiple Access (Codedivision MultipleAccess), which is a new and mature wireless communication technology developed in digital spread spectrum communication technology. The principle of CDMA technology is to process the information data with a certain signal bandwidth that needs to be transmitted with a high-speed pseudo-random code with a bandwidth much greater than the signal bandwidth, so that the bandwidth of the original data signal is expanded, and then modulated and sent out by the carrier. After demodulation, the receiver uses the exact same pseudo-random code to process it with the received bandwidth signal to separate the narrowband signal of the original information data from the wideband signal, that is, despread, so as to realize information communication.
Users and base stations in the system are distinguished by different codes and can share the same frequency band. Therefore, CDMA is a communication technology with high confidentiality, high spectrum utilization and high anti-interference ability. To learn more about service offers, click on the "****" customer service 222 below to answer for you.
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Anonymous users2024-02-05Code division multiple access: a new wireless communication technology.
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Anonymous users2024-02-04Features: High frequency band utilization, anti-interference, confidentiality, concealment, flexibility and anti-frequency.
rate of selective fading, etc.
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Anonymous users2024-02-031 CDMA is a kind of spread spectrum communication, which has the following characteristics of spread spectrum communication:
Strong anti-interference ability. This is the basic feature of spread spectrum communication, which is incomparable to all communication methods.
Broadband transmission, strong anti-fading ability.
Due to the use of wideband transmission, the power of the desired signal transmitted in the channel is much lower than that of the interfering signal, so the signal appears to be hidden in noise; That is, the power spectral density is relatively low, which is conducive to signal concealment.
The correlation of the spread spectrum code is used to obtain the user's information, and the ability to resist interception is strong.
2 In the spread-spectrum CDMA communication system, there are some new features due to the adoption of new key technologies:
A variety of diversity methods are used. In addition to traditional spatial diversity. Since it is the broadband transmission that plays the role of frequency diversity, and the RKE receiver technology is used in the base station and the mobile station, it is equivalent to the role of time diversity.
Voice activation technology and sector technology are adopted. Because the capacity of the CDMA system is directly related to the interference it receives, the use of voice activation and sectorization techniques can reduce the interference and increase the capacity of the whole system.
Soft switching assisted by a mobile table is adopted. It allows for seamless switching, ensuring the continuity of calls and reducing the possibility of dropped calls. The mobile station in the switching area can receive signals from multiple base stations through diversity, which can reduce its own transmission power, thereby reducing the interference to the surrounding base stations, which is conducive to improving the capacity and coverage of the reverse connection.
Power control technology is used, which reduces the level-level transmit power.
It has soft capacity characteristics. The number of channels that can be used can be increased by increasing the frame error rate during peak traffic periods. When the load of the adjacent cell is light and heavy, the cell with heavy load can reduce the transmit power of the pilot, so that the edge users of the cell can switch to the adjacent cell due to the lack of pilot strength, so that the burden is shared.
Good compatibility. Due to the large bandwidth of CDMA, the power is distributed over a wide spectrum, the power is low, and the interference to narrowband analog systems is small, so the two can coexist. That is, good compatibility.
CDMA has a high frequency utilization rate and does not require frequency planning, which is also one of the characteristics of CDMA.
CDMA's high-efficiency OCELP voice encoding. Voice coding technology is an important topic in digital communication. OCELP uses a code meter vector to quantify the difference and produces a signal with a variable output rate depending on the degree of voice activation.
This coding method is considered to be the most efficient coding technology at present, which greatly improves the capacity of the system under the premise of ensuring better voice quality. This vocoder has sequences of 8kbit s and 13kbit s. The 8kbit s sequence is variable from to to, and the 13kbit s sequence is variable from to.
Recently, another 8kbit SEVRC encoder has been introduced, which also has the characteristics of 8kbit S vocoder with large capacity, and the voice quality has also been significantly improved.
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Anonymous users2024-02-02Code division multiple access: a new wireless communication technology.
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Anonymous users2024-02-01Spread spectrum CDMA digital cellular systems share frequency band resources, and each cell in a CDMA cellular system shares a frequency band. From the perspective of frequency reuse, the relationship between the cellular group structure is greatly weakened. In CDMA systems, the cellular structure, including the sector structure, is considered to be the impact of multi-user interference after band resource sharing.
The signal bandwidth of the CDMA cellular system.
The determination of the spectrum bandwidth of a narrowband CDMA cellular system is based on the following considerations:
limitations on spectrum resources;
system capacity; multipath separation;
Spread spectrum processing gain.
Code division multiple access to cells and sectors of cellular systems.
Frequency division is used between spread-spectrum CDMA cellular systems, i.e., different CDMA cellular systems occupy bandwidth in different frequency bands. In a spread-spectrum CDMA cellular system, code sub-sites are used, that is, different cell and sector base stations are assigned different code patterns. Physical channels.
Links in the BS to MS direction are referred to as forward links, and links in the MS to BS direction are referred to as reverse links. Both the forward link and the reverse link are composed of code division physical channels.
Logical channels. Code division physical channels can be used to transmit information of different functions. Channels that are classified according to the different functions of the information being transmitted are called logical channels and <>
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