General Multicarrier System
A multicarrier system described herein indicates that one or more individual carriers are used as a group. FIGS. 1(a) and 1(b) show a signal transmission and reception method based upon a multiband radio frequency (RF).
For efficient use of multiband (or multicarrier), a technique has been proposed in which one medium access control (MAC) entity handles multiple carriers (e.g., several frequency allocation (FA)).
As shown in FIG. 1, one MAC layer in each of a transmitting end and a receiving end may manage several carriers for efficient multicarrier use. Here, for effective transmission and reception of the multicarrier, it is assumed that both the transmitting and receiving ends can transmit and receive multicarrier. Since frequency carriers (FCs) managed by one MAC layer do not have to be contiguous to one another, it may be flexible in view of resource management.
That is, a contiguous aggregation and a non-contiguous aggregation are all available.
Referring to FIGS. 1(a) and 1(b), PHY0, PHY1, PHY n−2, PHY n−1 denote multiband according to this technique, and each band may have a magnitude (bandwidth) of FA assigned for a specific service according to a predefined frequency policy.
For example, PHY0 (RF carrier 0) may have a bandwidth of FA assigned for a typical FM radio broadcast, and PHY1 (RF carrier 1) may have a bandwidth of FA assigned for cellular phone communications.
Each frequency band may have a different frequency bandwidth according to each frequency band characteristic. However, it may be assumed in the following description, for the sake of brief explanation, that each FA has A [MHz] magnitude.
Also, each FA may be represented as a carrier frequency for using a baseband signal at each frequency band. Hereinafter, each FA is referred to as “carrier frequency band” or, if not ambiguous, simply as “carrier” representing each carrier frequency band.
As shown in 3GPP LTE-A in recent time, to distinguish the carrier from a subcarrier used in a multicarrier technique, the carrier may be referred to as “component carrier.”
In this regard, the “multiband” technique may be referred to as “multicarrier” technique or “carrier aggregation” technique.
In order to send signals via multiband as shown in FIG. 1(a) and receive signals via the multiband as shown in FIG. 1(b), the transmitting and receiving ends are required to include RF modules, respectively, for transmission and reception of signals over the multiband. Also, in FIG. 1, the configuration of “MAC” may be decided by a base station regardless of downlink (DL) and uplink (UL).
Briefly explaining, this technique indicates that one MAC entity (hereinafter, simply referred to as “MAC” if not obscure) manages/runs a plurality of RF carriers (radio frequencies) for signal transmission and reception. Also, the RF carriers managed by the one MAC may not have to be continuous to each other. Hence, in accordance with this technique, it is more flexible in view of resource management.
In IEEE 802.16m system as one of wireless communication systems, the carriers may be divided into two carrier types from the perspective of a base station. For example, the carrier types may be divided into a fully configured carrier type (FCCT) and a partially configured carrier type (PCCT).
The FCCT indicates a carrier by which every control information and data can be sent or received, and the PCCT indicates a carrier by which only downlink (DL) data can be sent or received. Here, the PCCT may be used for services, such as an enhanced multicast broadcast service (E-MBS), which usually provides DL data.
From the perspective of a mobile terminal, assigned carriers may be divided into two types, for example, a primary carrier type and a secondary carrier type. Here, the mobile terminal may be allocated with one primary carrier and a plurality of subcarriers from the base station.
The primary carrier may be selected from the fully configured carriers. Most of essential control information related to the mobile terminal may be sent on the primary carrier. The subcarriers may be selected from the fully configured carriers or the partially configured carriers, and also additionally allocated in response to request of the mobile terminal or instruction of the base station.
The mobile terminal may send and receive not only every control information but also control information related to the subcarriers over the primary carrier, and exchange (transceive) data with the base station over the subcarriers. Here, the subcarrier, as a fully configured carrier, allocated to a specific mobile terminal, may be set to a primary carrier of another mobile terminal.
Multicarrier Switching
Multicarrier switching indicates a multicarrier mode for a terminal to switch a physical layer connection from a primary carrier to a partially configured subcarrier or a fully configured subcarrier. Here, the carrier switching of the terminal may be performed based upon instruction (indication) from a base station in order to receive E-MBS service at a subcarrier.
After being connected to the subcarrier for a specific time, the terminal may move back to the primary carrier. While the terminal is connected to the subcarrier for the specific time, the terminal does not have to maintain transmission or reception via the primary carrier.
Basic Multicarrier (MC) Mode
A basic multicarrier (MC) mode indicates a mode that a terminal operates using only one carrier. However, the terminal may support not only optimized scanning for carriers related to a multicarrier operation but also a primary carrier switching procedure.
Carrier Switching Operation for E-MBS Service
E-MBS service may be performed by a specific carrier (e.g., secondary carrier (E-MBS carrier)) other than a primary carrier. In a connected state with a base station, an E-MBS terminal having only one transceiver (i.e., a terminal operating in a carrier switching mode) may perform carrier switching from a primary carrier to another carrier to receive E-MBS data burst, E-MBS configuration message and E-MBS MAP, and carrier switching from the another carrier to the primary carrier to receive a unicast service from the base station.
The E-MBS terminal may perform a carrier switching operation based upon its E-MBS subscription information assigned from the base station to the terminal during a dynamic service addition (DSA) procedure. The E-MBS subscription information may be MSTIDs and FIDs, for example.
In an actual E-MBS environment, basic (default) E-MBS channels may be assigned (allocated) to every terminals subscribed in the E-MBS service, and the number of default E-MBS channels may be much more than the number of specific E-MBS channels (e.g., premium channels).                all the E-MBS terminals subscribe in all the default contents via default free channels.        Additionally, some premium users may subscribe in premium contents.        
In other words, E-MBS terminals subscribed in the premium contents may stay longer in the E-MBS carrier than terminals merely subscribed in the default contents.
FIG. 2 is a flowchart showing a carrier switching operation performed based upon terminal subscription information.
As shown in FIG. 2, it is assumed that a terminal 1 merely subscribed in default contents and a terminal 2 subscribed in the default contents and a premium content 2.
It is also assumed that E-MBS data bursts 1 and 3 are data for the default contents, E-MBS data burst 2 is data for a premium content 1, and E-MBS data bursts 4 and 5 are data for the premium content 2.
Referring to FIG. 2, the terminal 1 may stay at a primary carrier while a base station sends E-MBS data bursts 2, 4 and 5 (S201), and the terminal 2 may stay at a primary carrier while the base station sends E-MBS data burst 2 (S202). That is, the base station may allocate unicast resources to terminals, which have subscribed in the premium contents having the lowest unicast scheduling efficiency.
During free E-MBS service, a terminal may not need to perform a joining/leaving process at an upper layer. That is, in this case, when E-MBS terminal starts or ends E-MBS service reception, DSA/dynamic service deletion (DSD) process may not be performed. However, in the carrier switching mode, the base station must be known of whether a terminal is receiving the E-MBS service for efficient unicast scheduling. If the terminal is not receiving the E-MBS service, the base station may provide the unicast service to the terminal at the primary carrier at any time.
However, regarding the existing carrier switching operation, when the terminal subscribes in the E-MBS service and is in a connected mode with the base station, the terminal performs the carrier switching operation between a primary carrier and a secondary carrier (E-MBS carrier) regardless of the reception of the E-MBS service.
Here, in a state that the terminal subscribed in the E-MBS service is in the connected mode, if the terminal operates in the carrier switching mode even when not receiving the E-MBS service, the base station may not effectively schedule the unicast resource to the terminal (particularly, it may not guarantee QoS upon using VoIP), and the terminal may cause power consumption due to performing of the unnecessary carrier switching operation.