Current mobile communication systems follow market trends in that new mobile communication systems are structured with radio signal technology based on new communication systems so as to respond to demands for an increase in speed and capacity in communication. However, the introduction of a new mobile communication system requires that the existing mobile communication system be sequentially changed to the new mobile communication system in accordance with market trends without a significant change thereof, and that a plurality of types of the new mobile communication system be used in combination.
FIG. 1 is a diagram illustrating an example of a network configuration of a mobile communication system, in which two mobile communication systems of a 3G (Third Generation) system 100 and an LTE (Long-Term Evolution) system 200 as one of new mobile communication systems having increased speed and bandwidth compared with the 3G system, are provided concurrently.
For example, the 3G system 100 comprises: an RNC (radio network controller) 120 having a control function of controlling a radio network; an IP-RNC 120a; a BTS 110 having a function of managing and converting a radio signal; and an IP-BTS 110a. With radio signals based on a 3 G communication system, the BTS-110 and the IP-BTS 110a in the 3G system 100 are linked to a mobile terminal 1 (referred to as 3G-MS in FIG. 1).
The LTE system 200 comprises: an aGW (access gateway) 220 having a function of switching the radio signal and controlling a part of a radio network and a BTS 210 (referred to as an LTE-BTS in FIG. 1) having a function of managing and converting the radio signal. With an IP protocol, the LTE-BTS 210 in the LTE system 200 is linked to the aGW 220 as a higher-level device. Further, using a radio signal based on LTE-system communication, the LTE-BTS 210 can be linked to a mobile terminal 2 (referred to as LTE-MS in FIG. 1).
The 3G system 100 is linked to the LTE system 200 via an MSC (mobile Switching Center) 910 having a function of switching a radio signal of a core network 900 (referred to as CN), an IASA (Inter Access System Anchor) 920 that manages connection between different systems, and the aGW 220.
As the network example, the BTS 110 and the IP-BTS 110a are base transceiver stations (BTSs) that control the mobile terminal 1 (3G-MS) using a radio signal in conformity with a communication system of the 3G system 100. The LTE-BTS 210 is a base transceiver station that controls the mobile terminal 2 (LTE-MS) using a radio signal in conformity with a communication system of the LTE system 200, the mobile terminal 1 (3G-MS) and the mobile terminal 2 (LTE-MS) need to be simultaneously controlled by the same base transceiver station so that seamless communication of data is achieved between the mobile terminal 1 (3G-MS) and the mobile terminal 2 (LTE-MS) using radio signals based on different communication systems.
FIG. 2 is a diagram illustrating an example of a configuration of a base transceiver station (BTS), in which the BTS 110 in the 3G system 100 is depicted as a representative example.
The base transceiver station 110 includes a radio equipment control 111 (REC) that allows communication of data with the RNC 120 as a higher-level device, the mobile terminal 1 (3G-MS), and the radio equipment 112 (RE) that performs radio communication using a radio signal in conformity with the communication system for 3G system. The RE 112 is set for, e.g., an underground mall. Thus, the mobile terminal 1 can also be used at a place where radio waves do not sufficiently reach from the setting position of the REC 111. In general, a plurality of the REs 112 are disposed and are connected to one REC 111, via a communication link 8 using, for example, an optical fiber. The REC 111 transmits and receives data corresponding to the radio signal for the 3G system to the RE 112 via the communication link 8, thereby achieving communication of data with the RNC 120 as a higher-level device.
Regarding the installation manner of the base terminal station (BTS), in general, the radio equipment control (REC) and the radio equipment (RE) are set apart from each other and are connected with a one-to-n correspondence using optical fibers. The number of cases where a Common Public Radio Interface (CPRI) is used as an interface for the communication link between the REC and the RE, has increased. The CPRI Specification V2.1 discloses the details of the CPRI.
FIG. 3 is a diagram illustrating an example of an outline of a communication protocol defined by the CPRI.
As for data (IQ data), an “IQ Data” frame of Layer 2 and “User Plane” of Layer 3 are used. Further, an HDLC frame of “LAPB Protocol” of the Layer 2 and “Control & Management Plane” of the Layer 3 are used for transmission and reception of monitoring control data in order to maintain and monitor the RE 112. A “Vender Specific” frame of the Layer 2 is used for a specific purpose by a vender. Hereinbelow, a transfer frame for transmitting and receiving the data (IQ data) is referred to as an IQ data frame, a transfer frame for transmitting and receiving the monitoring control data is referred to as an HDLC frame, and a transfer frame for transmitting and receiving the “Vender Specific” data is referred to as a VS frame.
The details of the communication protocol defined by the CPRI are disclosed in the CPRI Specification V2.1. Herein, a description thereof is thus omitted.