With the development of the wireless communication industry, various wireless communication schemes have been proposed. In addition to the existing mobile communication network supporting a specific wireless communication scheme, it is possible to implement a mobile communication network supporting a wireless communication scheme different from the existing wireless communication scheme.
Therefore, the advent of a wireless environment, which includes the mixed mobile communication networks supporting different wireless communication schemes between them, is expected.
In such a wireless environment, it is necessary for mobile users to select and use a proper wireless communication scheme according to a wireless condition.
In line with this, a 3rd generation wireless communication system has been developed to perform high-speed and large capacity data communication as well as existing voice communication.
The 3rd generation wireless communication systems can be divided into systems of two standardization organizations, which include a 3rd Generation Partnership Project (3GPP), which is a European asynchronous standardization organization, and a 3rd Generation Partnership Project 2 (3GPP2), which is a synchronous standardization organization of the US. A typical scheme which is being discussed in the 3GPP organization is a Wideband Code Division Multiple Access (hereinafter, referred to as WCDMA) scheme, and a typical scheme which is being discussed in the 3GPP2 organization is a Code Division Multiple Access (hereinafter, referred to as CDMA) scheme.
The WCDMA scheme can be reclassified into WCDMA using the FDD scheme and WDCMA using the TDD scheme.
FIG. 1 is a block diagram illustrating a wire relay system of a conventional FDD wireless communication service system according to one embodiment. Referring to FIG. 1, the FDD is a scheme in which transmission and reception for communication are performed based on divided frequencies. First, RF downstream signals modulated in an FDD modem 2 of a Base Station (BS) 1 are converted into optical signals in a base station donor 3, and then the converted signals are delivered to the Remote Station (RS) 15 via an optical fiber by an optical transmitter 4. The downstream optical signals received from the base station donor 3 are input to a downstream RF signal conversion/amplification unit 11 by an optical receiver 10, and the input signals are delivered to wireless terminals via a duplexer 14 and an antenna 17.
Then, an FDD wireless communication service is performed. Upstream signals generated by the wireless terminals are input to a duplexer 14 of the RS 15 through an antenna 17 for frequency division. Then, the frequency-divided signals are amplified in a downstream RF signal reception/amplification unit 13, the amplified signals are input to the optical receiver 6 of the base station donor 3 via an optical receiver 12 and an optical fiber, and the resultant signals are input to the FDD modem 2 of the BS 1.
FIG. 2 is a block diagram illustrating a wire relay system of a conventional TDD wireless communication service system according to one embodiment. As shown in FIG. 2, the TDD is a scheme in which transmission and reception are divided according to different times and communication is performed. First, RF downstream signals modulated in a TDD modem 22 of a BS 21 are delivered to an optical transmitter 28 of a base station donor 23, and TDD sync signals from the TDD modem 22 are delivered to a TDD switching control transmitter 26 of the base station donor via a modem controller 24.
The TDD switching control transmitter 26 generates TDD switching control signals for switching the TDD sync signals at predetermined time, and the TDD switching control signals are converted into downstream optical signals, and the resultant signals are transmitted to the RS 25 through an optical transmitter 27. The optical receiver 32 of the RS 25 receives the downstream optical signals, the resultant signals are output by a TDD switching control signal distributor 33, and switching is performed according to the TDD switching control signals at corresponding times. Then, the TDD transmission scheme downstream signals received in an optical receiver 37 of the RS 25 are converted into RF signals, and the resultant signals are amplified. Therefore, the TDD transmission scheme service is provided to the wireless terminals through the antenna 39. In this case, for each wireless terminal receiving the provided TDD transmission scheme service, the times for downlink and uplink transmission and reception have been predetermined.
Accordingly, the wireless terminals and the BS perform communication within the predetermined times. In this case, the BS may assign some or all of the available time slots to wireless terminals performing communication.
As such, according to the FDD transmission scheme, frequencies for downlink and uplink transmission and reception between the BS and the wireless terminals are individually set, and the communication between wireless terminals and a BS is performed based on the set frequencies at all time.
Accordingly, an FDD scheme is suitable for use of macro-cell because it does not have a round-trip delay problem. The FDD scheme can provide a service suitable for a rapidly moving terminal due to a large cell radius.
On the other hand, in the FDD scheme, frequency bandwidths are symmetrical and are fixedly allocated. Therefore, the FDD scheme is limited in providing a variable asymmetric service.
Further, according to the TDD scheme, different time slots are assigned to uplink and downlink established between a BS and a specific wireless terminal. Therefore, the TDD scheme is suitable for provision of an asymmetric service. However, in the TDD scheme, when a cell radius becomes large, a guard time between transmission and reception increases due to the round-trip delay and thus transmission efficiency is reduced.
Therefore, the TDD scheme is not suitable for a cell with a large radius, such as a macro-cell, and each cell does not have an identical asymmetry rate under the multiple cell environments in the TDD scheme. Therefore, in the TDD scheme, the same frequency interference increases between terminals located in edges of adjacent cells.
Accordingly, a next generation wireless communication service requires a high-speed data rate to be provided to rapidly moving terminals, so that it is necessary to research a system utilizing the advantages of TDD and FDD scheme.