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OFDMA is an attractive multiple access technique for packet-based mobile broadband wireless access for beyond 3G and 4G systems. Radio resource allocation in OFDMA can exploit multiuser diversity to increase system capacity by implementing opportunistic scheduling techniques. This paper presents a new opportunistic scheduling scheme for OFDMA-based...
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... increasing demand for high transmission rates in wireless communication systems brought into play the need for new transmission techniques. However, high transmission rates may result in sever frequency selective fading and intersymbol interference (ISI). Orthogonal Frequency Division Multiplexing (OFDM) has recently been proposed as an effective multi-carrier solution for broadband wireless transmission [1]. In an OFDM system, the high data rate stream is transformed into a number of lower rate com- ponents. Each of the OFDM signal components is modu- lated onto a distinct subcarrier. The bandwidth of the low rate component is narrower than the coherence bandwidth of the channel, thus the transmission in each subcarrier ex- periences flat fading. Furthermore, orthogonal subcarriers cause OFDM systems to have a higher spectral efficiency. These advantages made OFDM to be adopted for the physical layer in many current and future high speed wireless communications systems such wireless local area networks (WLAN), wireless metropolitan area networks (WMAN), and mobile broadband wireless access (MBWA) standards. In multiuser environment, OFDM can also be applied producing a highly flexible, efficient high speed communications system. Since Wahlqvist et al [2] studied multiuser OFDM, intense research was carried out aiming to find im- proved and flexible multiple access methods other than tra- ditional time division multiple access (TDMA) or frequency division multiple access (FDMA) techniques (which em- ploy fixed and predetermined time-slot or subcarrier allocation schemes). Orthogonal frequency division multiple access (OFDMA) is a promising multiple access scheme that has recently attracted enormous research interest [4]-[13]. (OFDMA is a multiple access scheme which is based on OFDM with the only exception that the OFDM symbol is composed of data from multiple users sharing the wireless system.) Here, the base station is responsible for deciding how the available subcarriers will be distributed among different users. In this paper, we consider the subcarrier management problem in the downlink of OFDMA wireless multimedia networks for delay-constrained traffic. The problem is divided into two sub-problems: the subcarrier allocation problem and the subcarrier assignment problem. Based on the principles of multi-user diversity [14], we propose an opportunistic subcarrier allocation algorithm that uses the channel state information and the delay information of different downlink flows to calculate the number of subcarriers to be assigned to each active user in the system. The algorithm also attempts to guarantee the QoS required by these users. We also propose an opportunistic algorithm for the subcarrier assignment problem. The proposed algorithm monitors the deadline violations in all queues, and ensures fairness among different users in their service rates. This is achieved by distributing the deadline violation occurrence among all flows evenly. The rest of this paper is organized as follows: Section 2 defines the OFDMA network model. Then we describe the multiuser scheduling problem in such networks in section 3 and include a survey of related work. In section 4, the proposed subcarrier allocation and subcarrier assignment algorithm are introduced. We report the results of extensive set of simulation experiments in section 5. Section 6 summarizes the main findings of the paper. We consider the downlink scheduling of a single cell in cell-structured OFDMA-based system. The cell is equipped with a base station which is responsible for coordinating the simultaneous transmissions of N mobile users over S OFDM subcarriers. Inter-cell interference is not taken into consideration. OFDMA adds multiple access to OFDM by allowing a number of users to share an OFDM symbol. Therefore, an OFDMA transmitter employs a subcarrier allocation and assignment function instead of the serial to parallel conversion used in OFDM systems to split the single user’s stream into a set a parallel low rate streams. The rest of OFDMA system is the same as an OFDM system as shown in Figure 1. Adaptive modulation is used to transmit data over individual subcarriers with different gains yield- ing significant performance improvement. The base station is responsible for informing each user terminal which subcarriers are assigned to it via a set of subcarriers (or time slots in a frame) reserved for control functions. The receiver then does the reverse operations at the transmitter and the data sent to this user is retrieved by demodulation of the user’s assigned subcarriers. High speed wireless standards are usually operated at high frequencies. High frequency channels, like those used in OFDMA-based networks, are characterized by their time-varying, frequency-selective fading nature. Channel gains vary from subcarrier to subcarrier for a single wireless terminal due to multipath propagation. Besides, channel gains of each subcarrier vary over time for the same user terminal, due to the movement of the terminal and other ob- jects within the surrounding area. At a given time, some subcarriers suffer severe fading, while others have a good response. In this case, if the channel information is available, it is more efficient to transmit data only over those subcarriers having a good response with high transmission rates. Furthermore, channel gains of a specific subcarrier vary from wireless terminal to wireless terminal due to sta- tistical independence. This implies that certain subcarriers that are in deep fade for some users are not necessarily bad for others since the user channel fading characteristics are uncorrelated for different users. Hence, selection of good subcarriers for one user may not necessarily block other users from accessing their good subcarriers. This gives the general motivation to develop a resource allocation frame- work that exploits multiuser diversity to allocate and assign an active user its best subcarriers, and hence increase the efficiency of channel utilization. In OFDMA-based networks, the scheduler is responsible for dividing the set of subcarrier available to the base station into a number of mutually disjoint subsets of subcarriers. Each subset is assigned to a certain user for a certain period of time (scheduling interval). Recently, there has been intensive research on subcarrier and bit allocation in multiuser OFDMA systems [4]-[13]. Those algorithms can be categorized as static and dynamic allocation algorithms. Static subcarrier management schemes depend on tra- ditional multiple access schemes, such as Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA), as a mechanism for distributing the subcarriers in multiuser OFDM networks. In OFDM-TDMA, one of the users is assigned all the subcarriers for the entire scheduling interval, whereas in OFDM-FDMA, each user is permanently assigned one or several predetermined subcarriers. Thus, both OFDM-TDMA and OFDM-FDMA are not capable of adapting to the channel gain variations. As a consequence, any fixed assignment of subcarriers to terminals will waste system resources in the form of either power or bit rate [3],[5]. Recently, dynamic radio resource management schemes that consider the users’ instantaneous channel conditions have attracted enormous research interest. This is due to the significant overall system efficiency increase obtained when variations in channel gains among users (multiuser diversity) is exploited. These schemes vary in their design and performance objectives, however, they can generally be classified into two main categories: the first set of schemes target the minimization of total power subject to a minimum achievable throughput (total or per user), while the second set of schemes target the maximization of throughput subject to maximum power (total or per user). Many schemes known as bit loading algorithms have been suggested [3]-[6]. They adapt transmission power or bit rates optimally to the channel gains of different subcarriers, where either a feasible overall bit rate or a maximum available transmit power is given. They are based on a result from information theory describing how to distribute transmission power over a set of subcarriers with different channel gains in order to maximize the channel’s capacity. This is known as the water filling principle first discussed by Shannon [15]. Wong et al [3] addressed the problem of minimizing the transmitted power at a given bit rate per terminal. Subcarrier and bit allocation was done dynamically through the use of nonlinear optimization with integer variables. A modifi- cation to Wong’s algorithm was proposed in [4]. The proposed extension allows each user to specify its individual QoS requirements, defined in terms of bit rate and bit error rate. The scheme distributes subcarriers and transmit power among multiple users according to their QoS requirements. An alternative problem of maximizing the overall bit rate of multiple wireless terminals while the transmit power is upper bounded have been ...
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... an OFDMA transmitter employs a subcarrier al- location and assignment function instead of the serial to par- allel conversion used in OFDM systems to split the single user's stream into a set a parallel low rate streams. The rest of OFDMA system is the same as an OFDM system as shown in Figure 1. Adaptive modulation is used to transmit data over individual subcarriers with different gains yield- ing significant performance improvement. ...
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Citations
... We will see in this paper that such a per-block definition of the problem naturally leads to converting the delay constraint into a rate constraint which further eases the channel awareness at the scheduler level, as discussed in Section 3. As a remark, the proposed solution also applies to nonequal delay constraints, but this is out of the scope of this paper. Such a goal has already been investigated in the literature [6], but usually arbitrarily combines Delay-constrained and Channel-aware metrics. ...
This paper proposes a preemptive scheduler that takes back resource previously allocated to best effort traffic users for minimizing the drop rate of delay constrained traffic users. An online implementation with low complexity is proposed, where the channel and QoS aware preemption metric takes into account the benefit for the drop rate of the delay constrained traffic and the cost on the fairness of the pre-allocated best effort traffic. By inverting the state of art order of the allocation of delay constrained and best effort traffic, we show that the fairness-throughput tradeoff curve of the best effort traffic is improved with no degradation on the drop rate of the delay constrained traffic. This sched-uler is particularly relevant in cellular networks mixing safety-related and non-safety related (data) traffic, such as LTE for trains, tram, buses or cars.
... The classic sum-rate maximization algorithm and proportional fairness (PF) algorithm can not support delay sensitive services such as voice and real-time video, because they do not account for packet delay and could result in poor delay performance. Therefore, much literature investigated the radio resource management policy considering packet delay constraint of RT users and trying to improve system throughput of NRT users as well [4][5][6][7][8][9]. In Ref. [4], two examples of delay-utility functions were depicted and then a scheduling algorithm called ''the U'R rule'' was proposed, which aimed to maximize the time-averaged total delay-utility in wireless networks. ...
... In Ref. [4], two examples of delay-utility functions were depicted and then a scheduling algorithm called ''the U'R rule'' was proposed, which aimed to maximize the time-averaged total delay-utility in wireless networks. A scheduling algorithm for delay sensitive traffic with packet deadline in OFDMA system was proposed in Ref. [5], but the algorithm could not deal with the mixture of RT and NRT services. Afterwards, in Ref. [6], a downlink scheduling algorithm in OFDMA systems for the RT and NRT mixed services was proposed, which was based on the delay-utility function and channel state information. ...
In this paper, a novel “delay- and utility-oriented (DUO)” resource allocation algorithm for the mixture of real-time (RT) and non-real-time services in orthogonal frequency division multiple access systems is proposed. The proposed DUO algorithm considers delay-utility function and rate-utility function simultaneously, scheduling RT packets approaching the deadline first and then achieving as much aggregate rate-utility as possible. Simulation results reveal that it can not only satisfy RT users’ delay requirements in terms of packet drop ratio, but also obtain much more aggregate rate-utility for mixed services than other reference algorithms. Besides, the rate-utility fairness of all users is also improved substantially.
... Our algorithm is a feedback base Opportunistic (i.e. channel-aware) downlink scheduling meant for scheduling bandwidth for Mobile TV users, existing related opportunistic scheduling are [2], [8], [4], [5], [10] and [7]. ...
... [2], [7] are more related to our downlink scheduling algorithm for video traffic, [2] In term of better throughput performs well, packet dropping is less and it is fair in delay distribution. it does it scheduling in subcarrier allocation and assignment, for fairness and priority tie purpose, users with more packet dropped are favoured and does not give precedence to user with poor Channel Quality, [7] designs a queue and channel aware downlink scheduler (a scheduler priority-based) algorithm for WiMAX, where all of the QoS metrics, such as channel, queue, non-urgent and urgent data status are translated to priority metric by a black-box formula in the study, but it is not fair to all users, there is no CQI reporting metrics. ...
... Qos, throughput, fairness and priority) like ours, it take cares of users with bad/worst channel condition. In this paper we referred to related Opportunity Scheduling and others scheduling as blind algorithms especially [2]. The blind algorithms do not offer pragmatic solution for scheduling a synchronized real time (basic service in the form of programs with mass appeal examples, live sporting events and real-time news and non real time or live programs example pay-toview prime time programs targeting a given user group with specific interests), multi traffic applications for mobile TV. ...
With high speed access network technology like WIMAX, there is the need for efficient management of radio resources where the throughput and Qos requirements for Multicasting Broadcasting Services (MBS) for example TV are to be met. An enhanced feedback-base downlink Packet scheduling algorithm that can be used in IEEE 802.16d/e networks for mobile TV “one way traffic”(MBS) is needed to support many users utilizing multiuser diversity of the broadband of WIMAX systems where a group of users(good/worst channels) share allocated resources (bandwidth). This paper proposes a WIMAX framework feedback-base (like a channel-awareness) downlink packet scheduling algorithm for Mobile TV traffics in IEEE806.16, in which network Physical Timing Slots (PSs) resource blocks are allocated in a dynamic way to mobile TV subscribers based on the Channel State information (CSI) feedback, and then considering users with worst channels with the aim of improving system throughput while system coverage is being guaranteed. The algorithm was examined by changing the PSs bandwidth allocation of the users and different number of users of a cell. Simulation results show our proposed algorithm performed better than other algorithms (blind algorithms) in terms of improvement in system throughput performance. Doi: 10.12777/ijse.5.1.55-62 [How to cite this article: Oyewale, J. and , Juan, L.X.. (2013). An Enhanced Feedback-Base Downlink Packet Scheduling Algorithm for Mobile TV in WIMAX Networks. International Journal of Science and Engineering, 5(1),55-62. Doi: 10.12777/ijse.5.1.55-62]
... Currently available uplink (UL) scheduling schemes at Subscriber Stations (SSs) in WiMAX experience resource wastage and high access delay for the different present service flows in WiMAX [4]. There have been a lot of researches going on the designing of an efficient scheduling algorithm [5], [6], [7], [8] for the optimized usage of the bandwidth, but mostly are not capable to utilize resources with low computational overhead. Thus, main focus is done on developing and modifying a scheduling algorithm which will highly optimize the usage of the resources in WiMAX networks and will be computationally simple. ...
... The first condition is, when the queue of that connection is full and second condition is, while collecting the data packets of a frame and the frame gets overflow. In this case, the data packets of lower priority like packets of BE and nrtPS are dropped first and then the higher priority connection packets are dropped [5], [6]. This is done by forming virtual frame and storing the packet in one of those frames instead of storing them in the queues. ...
High mobility and need for data access with high speed, brings the Broadband Wireless Access (BWA) like WiMAX in forefront. IEEE Standard does not offer any standard scheduling algorithm and till now, it is an open issue for research. The objectives of the scheduling are resource optimization with high throughput and low computational complexity. In this paper, we propose a scheduling algorithm based on a virtual frame concept for the Subscriber Stations (SSs) of the WiMAX. Simulations are performed in Network Simulator 2 (NS2) for verification of the proposed scheme. The simulation results show that by using the proposed Advanced Scheduler (AS) approach the response time to BS decreased to 16.02% in comparison to queue length aware approach. The proposed approach optimizes the usage of the bandwidth and resources in the WiMAX networks by including intelligence for different service flows at the SSs. Moreover, it does fair management of lower class services such as nonreal time Polling Service (nrtPS) and Best Effort (BE) in comparison to Unsolicited Grant Service (UGS) and real time Polling Service (rtPS).
... By determining the MCS (Modulation and Coding Scheme) and transmission power, an optimized multicast strategy maximizes the video quality under resource constraints is achieved in [10], in which the scalable video multicast is considered as a best-effort service. Focusing on opportunistic scheduling of delay sensitive traffic such as VoIP and video streaming in OFDMA-based wireless networks, the authors determine how many subcarriers should be assigned to each user according to users' average traffic rate and channel state, and allocate subcarriers for maximizing the total system throughput in [11]. In [12], an online resource allocation algorithm is proposed on the foundation of a two-layer Lagrangeduality method with heterogeneous delay and fairness consideration. ...
In this paper, we propose a packet scheduling algorithm for downlink OFDMA wireless systems in which users have heterogeneous traffic. The proposed scheduling algorithm not only focuses on channel state and fairness but also takes the users' queue length into consideration. With the idea of beta deadline parameter, we convert the delay bound of real-time traffic to date rate domain QoS parameter, and extend the idea for non real-time traffic with the minimum average throughput requirement. According to the subscribers' QoS parameter, we divide the whole band into chunks with different size flexibly. Chunks are allocated to users in accordance with the scheduling rule. Simulation results demonstrate that the proposed scheduling algorithm can acclimatize itself to active user number in the system and the users' requirements for radio resource. Its performance in terms of spectral efficiency, packet loss ratio, and the real-time traffic packets' delay, is better than algorithms with fixed chunk size dividing.
... Some scheduling algorithms have been proposed for multicarrier systems. In [8] an Opportunistic Scheduling (OS) algorithm is proposed. This scheduling algorithm is quite complex due to the fact that it performs resource assignment and resource allocation in different steps, resulting in a more complex scheduling algorithm. ...
We consider in this paper downlink scheduling at the Medium Access Layer (MAC) layer for delay sensitive traffic in wireless systems based on Orthogonal Frequency Division Multiple Access (OFDMA). We refer in particular to next generation wireless systems such as 3GPP-LTE. We propose an Opportunistic Packet Loss Fair (OPLF) scheduling algorithm based on calculating a simple dynamic priority function which depends on the Head of Line (HOL) packet delay, the packet loss rate (PLR) and the achievable instantaneous downlink rate of each user. This algorithm overcomes the main limitations of existing algorithms, achieving better performance than state-of-the art algorithms, such as Modified Largest Weighted Delay First (M-LWDF), Proportional Fair (PF), and Packet Loss Fair (PLF), in terms of throughput, PLR and fairness among users.
... Enhancements to the PF scheduler are further proposed in [22,23,31,32] in order to support QoS. In particular, Ryu et al. [23] propose an algorithm, called UEPS, that uses a time-utility function as a scheduling urgency factor jointly with the status of the current channel as an indicator of the radio resource usage. ...
... Hou et al. propose in [31] an algorithm to dynamically tune the parameters of the PF algorithm: by using different time windows to estimate the throughput they show that it is possible to differentiate the queuing delay. On the other hand, Khattab and Elsayed [32] split the scheduling decision into two sub-problems: the OFD-MA subcarrier allocation followed by the subcarrier assignment. Won-Hyoung et al. [29] propose a scheduler for multiple traffic classes that is an extension of Modified Largest Weighted Delay First (M-LWDF) scheduler originally proposed in [30]. ...
The IEEE 802.16 is a standard for fixed and mobile Broadband Wireless Access (BWA). In this paper, we deal with two key challenges of 802.16-based networks. First, terminals close to cell edge experience poor channel quality, due to severe path-loss and high interference from concurrent transmissions in nearby cells. To address this issue, we propose a framework based on a static partitioning of bandwidth into chunks with different transmission power levels. Terminals with impaired channel conditions can then benefit from being allocated a higher amount of transmission power than the others. Secondly, transmissions should be scheduled according to Quality of Service (QoS) requirements to keep users with real-time video or voice calls satisfied, while best-effort connections should fairly share the remaining capacity. To this aim, we propose a scheduling algorithm, called Power-aware Opportunistic Downlink Scheduling (PODS), that aims at meeting both the QoS and fairness requirements, while taking into account the different power levels of the bandwidth chunks. The performance of the proposed scheduler is assessed through detailed packet-level simulation in realistic scenarios and compared with well-known scheduling algorithms. Results confirm that PODS is able to exploit power boosting to provide real-time connections with the desired level of QoS, irrespectively of their MSs’ channel quality.
... Much of the research based on PF scheduling for OFDMA systems has focused on finding a good compromise between fairness and high system throughput with some QoS constraints, such as minimum throughput[3]and BER[6]. Some recent works have considered PF scheduling with delay QoS constraints[7], but they do not present analytical results describing the tradeoff between throughput and delay QoS for OFDMA systems. In our previous work[8], we studied the effect of user multiplexing on delay QoS performance in single channel systems over flat fading channels. ...
... Static allocation is simpler, but some of the assigned subcarriers may be experiencing deep fades. According to the proposed technique, each user can apply an individual generalized prefix [28]. Therefore, the system performance can be increased for both static and dynamic allocation systems. ...
All practical orthogonal frequency-division multiplexing (OFDM) systems require a prefix to eliminate intersymbol interference (ISI) at the receiver. Cyclic prefix (CP) and zero padding are well-known prefix construction methods, with the former being the most employed technique in practice due to its lower complexity. In this paper, we construct an OFDM system with a generalized CP. It is shown that the proposed generalized prefix effectively makes the channel experienced by the packet different from the actual channel. Using an optimization procedure, lower bit error rates (BERs) can be achieved, outperforming other prefix construction techniques. At the same time, the complexity of the technique is comparable with the CP method. The presented simulation results show that the proposed technique not only outperforms the CP method but is more robust in the presence of channel estimation errors and mobility as well. Therefore, the proposed method is appropriate for practical OFDM systems.
... T . -d,(t)+i (5) Where �TjE [O,Tj] is the guard time ahead of the deadline Tj.And for non-real-time services(6) Where Rmin denotes minimum reserved traffic rate and the average transmission rate at time t is usually estimated over a window size to:[Jy)= [Jy -1 )(1-1 /t)+ R Y -1 )/t (7) First the number of slots is estimated for each SF[4] ,[10]: ...
Scheduling is an essential component in WiMAX networks for efficient use of radio resources. In this paper, we propose a review of some scheduling algorithms for OFDMA-based WiMAX networks, MAX-SNR scheduling, Proportional Fairness scheduling (PFS) and a novel cross-layer scheduling algorithm (CACBq). The CACBQ algorithm takes into account both QoS and channel condition of users in its decisions. Simulation results are presented in two scenarios to achieve better evaluation of the performance of these schemes. CACBQ algorithm outperforms other algorithms in delay and packet loss rate for real-time services. However, MAX-SNR algorithm has the best throughput.
