or secondary is relative rather than abstract. Multiple mobile stations with different primary carriers may also share the same physical carrier as their secondary carrier. The following multi-carrier operation modes may be supported in various deployment scenarios: Carrier Aggregation: a multi-carrier mode in which the MS maintains its physical layer connection with the primary component carrier while transmitting or receiving data on the secondary carrier(s). The resource allocation to an MS may span the primary and one or more secondary carriers. The link adaptation mechanisms will then rely on channel quality measurements on primary and secondary carriers. In this mode, the system may assign secondary carriers to an MS in the downlink and/or uplink asymmetrically based on MS capability, system load (i.e., for static/ dynamic load balancing), peak data rate, or QoS requirements. Carrier Switching: a multi-carrier mode in which the MS switches its physical layer connection from the primary to the (partially or fully-configured) secondary carrier based on the serving base station's instruction in order to receive E-MBS data on the secondary carrier. The MS will connect to the secondary carrier for the specified time interval before returning to the primary carrier. When the MS is connected to the secondary carrier, it is not required to maintain connection with the primary carrier. Basic Multi-carrier Mode: an operating mode in which the MS uses only one component carrier for normal operation, but supports the primary carrier switching as well as optimized scanning of carriers involved in multi-carrier operation. 11.2 Sub-carrier alignment and use of guard sub-carriers The MS may support at least one of the above multi-carrier modes if it is multi-carrier capable. The following features are common to all multi-carrier modes: The system designates N standalone fully-configured carriers, each containing synchronization, broadcast, multicast, and unicast control channels required to support a single-carrier MS. Eac