FDMA (frequency division multiple access)

FDMA (frequency division multiple access) is the assigned to wireless cellular phone communication band is divided into 30 channels, each channel can transmit voice calls, digital service and digital data. Frequency division multiple access is simulated senior mobile phone services (AMPS in one of the basic techniques in North America, is the most extensive application of cellular phone system. Using frequency division multiple access, each channel every only assigned to a user. Frequency division multiple access is also used in full access communication system (TACS).

Basic introduction

FDMA Division Multiple Access (been) is one of the data communication technology, i.e., different users in the same and the distribution of time Frequency with different channel. According to this kind of technology, put in frequency division multiplexing transmission system of centralized control frequency allocated to users according to requirements. Compared with the fixed allocation system, frequency division multiple access to channel capacity can be dynamically switched according to requirements.

In FDMA system, distribution give users a channel, namely a pair of spectrum, a former spectrum used to channel that base station to the mobile station direction channel, another is used to reverse channel namely mobile station to base station direction channels. This system of communication stations must simultaneously transmit and receive several different frequency of the signal, any two mobile user communication between must pass stations relay, therefore it must be simultaneously occupy 2 channel (2) of the spectrum can realize full-duplex communication.

Previous analog communications system shall be by FDMA. Frequency division multiple access (FDMA) is using FM multi-access technologies. Business channel in different frequencies assigned to different users. If TACS system, AMPS system, etc. Frequency division multiple access is the communication system of total band fan.if equally spaced channel (also called channel) assigned to different users. These channels fold each, its width should be able to transmit all digital voice messages, while in adjacent channel between no apparent crosstalk.

characteristics

FDMA refers to different mobile station (or mobile phone) occupy different frequencies, namely each mobile platform occupies a frequency channel communication or communication. Because each user use of different frequency channel without interfering with each other, so. This is simulated carrier communication, microwave communications, satellite communication, but also the basic technology of the first generation of simulation mobile communication technology, basic early mobile communication more using this approach. Since each mobile users communicate occupy a frequency, a channel, the bandwidth utilization rate is not high. Along with the rapid development of mobile telecommunication, soon shows its capacity lack faults.

FDMA - in frequency division multiple access, different address users occupy different frequencies, i. e., adopting different carrier frequency, through the filter selection signal and inhibit useless interference, each channel in time can be used at the same time. Frequency division multiple access technology more mature, the first generation cellular mobile phone system USES is FDMA technology. Analog cellular mobile phone system all USES frequency division multiple access technology.

Satellite communication of multi-access connection technology and multiplexing technique is the signal segmentation application of the theory. They are very similar, but have difference. Multi-access technology is more TongXinZhan rf signal in frequency channel on the multiplexing, in order to reach more TongXinZhan multilateral communication between the purpose; And a TongXinZhan multiplexed multi-channel group of signal in frequency channel on the multiplexing, in order to reach two stand between the bilateral multi-channel communication purposes.

FDMA frequency division multiplexing multi-access way.this way is each earth station to allocate a special carrier, and all, earth station of the carrier to be different from each other, in order to carrier does not interfere with each other, between them, have enough space. Namely frequency division multiplexing - FM way - frequency division multiple access (FDM - FM - connecting FDMA), here, first by long distance phone signals to carrier terminal, press service frequency division multiplexing FDM ways to reuse in 60 road signal, the whole baseband standard baseband includes 5 base groups, each base group have 12 words road, will they press preassigned ways assigned to a earth station. Then put 60 road group with FM mode modulation signal to the assigned to earth station on the site of the carrier antenna system to the satellite launch. Through satellite uplink frequency repeater will on converting downlink, concurrent to stations, these earth station will receive the signal demodulation gets 60 road group of signals, starting from the group of signal filter to this site of base of signal.

purpose

Frequency division multiplexing aims to increase bandwidth utilization. Usually, in communication system, channel can provide the bandwidth tends to transmit signals than all the much needed to bring it. Therefore, only a channel transmission way signal is very wasteful. In order to make full use of channel bandwidth, thus puts forward channel frequency division multiplexing problem.

After the merge the reuse of the signal, in principle can be in the channel transmission, but sometimes to make better use of channel transmission characteristics, still can another modulation.

In the receiver, can use the corresponding bandpass filter (BPF) to distinguish from each signal spectrum. And then, through their respective coherent modem will restore rostrum modulation signal.

Frequency division multiplexing systems the biggest advantage is channel multiplexing rate is high, allow the reuse of poems, dropping very convenient also. Therefore, it becomes an analog communications of the major a multiplexing method. Especially in the cable and microwave communication system used widely. Frequency division multiplexing system's main shortcoming is equipment production is more complex, because filter pieces characteristics insufficient ideal and channel exists inside nonlinear and produce road interference between.

Related technologies

Digital mobile communications network's main multi-access way is FDMA, TDMA system (GSM, DAMPS). In the spectrum efficiency is about three times the simulation system, limited capacity, In voice quality 13kbit/s coding is difficult to achieve the landline telephone level, FTDMA system business comprehensive ability is higher, data and voice comprehensive, but terminal access rate limited (maximum 9.6 kbit/s TDMA system without soft handoff function, and therefore easy to drop words, affect the service quality z; TDMA system of international roaming agreement has yet to be further improvement and development. Thus TDMA not modern cellular mobile communication, and the best wireless access code division multiple access technology completely suitable for modern CDMA mobile network required large capacity and high quality, integrated business, soft handoff, international roaming etc.