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AssigneeLucent Technologies Inc.
InventorsDaniel Matthew Andrews, Lijun Qian, Aleksandr Stolyar
Estimating the term…
A new approach is described for scheduling uplink or downlink transmissions in a network having remote terminals communicating with a central hub. The scheduler keeps track of a token count. The token count for a given remote terminal is incremented by a target amount in each pertinent timeslot, but is also decremented each time that the remote terminal is served. The amount of the decrement for one timeslot is the amount of data served, i.e., transmitted to or from the remote terminal, in that timeslot. In exemplary embodiments of the invention, the target amount by which T is incremented depends on the current value of T. Whenever the token count is non-negative (i.e., whenever it has a positive or zero value), the target amount is a desired floor, or lower limit, on an average amount of data delivered to or from the given remote terminal in one timeslot. Whenever the token count is negative, the target amount is a desired ceiling, or upper limit, on the same average amount of data delivered. In each timeslot, each remote terminal is assigned a weight proportional to a product of at least two factors: a function relating the individual remote terminal to overall network performance, and at least one increasing function of the token count. Each time a scheduling decision is made, the scheduler selects for service that remote terminal having the highest weight.
A method for scheduling transmissions between a central hub and a plurality of remote terminals of a communication network, comprising:
Dependencies are inferred from the claim text.
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Allocation or scheduling criteria for wireless resources: based on resource usage policies
Traffic control in data switching networks: queue scheduling
By attributing bandwidth to queues: quantum based scheduling, e.g. credit or deficit based scheduling or token bank
Queue service order: weighted service order
Term end not estimated
This invention relates to the scheduling of communicative transactions between a central hub in a communication system, and remote terminals that are served by the hub. More particularly, the invention relates to scheduling downlink transmissions from a base station to mobile stations of a wireless communication system.
Many communication networks include an arrangement in which a centralized node, or “hub,” communicates with a group of non-centralized terminals, which are here referred to as “remote terminals.” If the remote terminals communicate with the hub over a common channel, it is possible for the communications between one remote terminal and the hub to interfere with communications between other remote terminals and the hub. To prevent such interference, it is often desirable to employ the techniques of time-division multiplexing. According to such techniques, each remote terminal has an assigned timeslot during which it may communicate with the hub by sending or receiving transmissions without interference from competing remote terminals within the group.
In some fields, the process of determining which remote terminal should be assigned a given timeslot is referred to as “scheduling.” That terminology will be adopted here. Similarly, an entity, typically resident at the hub, that makes the scheduling determination for each timeslot will be referred to here as a “scheduler.” The simplest form of scheduling is “round robin” scheduling, in which the remote terminals are scheduled in a fixed order, and typically for equal durations. The scheduler repeatedly cycles through the remote terminals in the fixed order.
FIG. 1 is a simplified schematic drawing of a cell of a wireless communication system, including mobile stations, a base station, and queues of buffered packets within the base station.
FIG. 2 is a flowchart of an illustrative sequence of steps performed by a scheduler during the n'th timeslot according to the invention in one embodiment.
FIG. 3 is a number line illustrating the effect of the token counter for a given remote terminal according to the invention in an illustrative embodiment. Each point on the number line represents a possible value for the token counter. The present value of the token counter, as represented by a point on the number line, is referred to here as the “operating point.”
Initially, it should be noted that it is convenient to adopt a convention in which transmission rates are expressed in bits per timeslot, because under such a convention, the amount of data delivered in a given timeslot is numerically equal to the rate over that timeslot. We will adopt that convention in the following discussion. Accordingly, it should be borne in mind that when the amount of data served or the token count is said to be incremented or decremented by a “rate,” what is actually meant is the amount of data delivered at that rate in one timeslot.
Our scheduling method has specific applications to the scheduling of packet transmissions from a base station to mobile stations of a CDMA network. Accordingly, the illustrative embodiment described below is implemented by a scheduler in such a network. However, our scheduling method is more general in its range of applicability, and we envisage other useful applications in communication networks of other kinds, including both wired and wireless networks. In particular, our method is applicable not only for scheduling downlink transmissions, but also for scheduling uplink transmissions in a CDMA or other wireless network.
In the case of uplink scheduling, the queues to be served will reside in the individual mobile stations rather than in the base station, and the mobile station will report both channel information and the queue length to the base station at prescribed times. In one approach, the mobile station reports channel information by sending pilot signals to the base station. From the pilot signals, the base station evaluates the channel conditions and selects an appropriate DRC accordingly. In one of various alternative approaches, the mobile station uses a downlink signal to estimate the quality of the uplink channel, and sends a corresponding DRC back to the base station.