Abstract
Single carrier frequency division multiple access (SC-FDMA) is a promising uplink transmission technique that has the characteristic of low peak to average power ratio. The mobile terminal uplink transmission depends on the batteries with limited power budget. Moreover, the increasing number of mobile users needs to be accommodated in the limited available radio spectrum. Therefore, efficient resource allocation schemes are essential for optimizing the energy consumption and improving the spectrum efficiency. This chapter presents a comprehensive and systematic survey of resource allocation in SC-FDMA networks. The survey is carried out under two major categories that include centralized and distributed approaches. The schemes are also classified under various rubrics including optimization objectives and constraints considered, single-cell and multi-cell scenarios, solution types, and perfect/imperfect channel knowledge-based schemes. The advantages and limitations pertaining to these categories/rubrics have been highlighted, and directions for future research are identified.
TopIntroduction
Cellular wireless technologies are continuously developing and wireless systems are upgraded to meet the increasing demand of the wireless users and improve the energy as well as spectral efficiency of the systems. Recently, for this purpose, Single Carrier Frequency Division Multiple Accesses (SC-FDMA) has got attention of researchers and industrial analyst for uplink communication. Currently, it is adopted as a multiple access scheme for LTE (Long Term Evolution) uplink transmission (Sofer & Segal, 2005; Wong, Oteri, & McCoy, 2009) and is assumed as a strong candidate for the uplink transmission in the next generation wireless networks.
To fulfill the high demands of capacity in wireless networks, Orthogonal Frequency Division Multiple Access (OFDMA) performs well for downlink whereas SC-FDMA is efficient for uplink wireless networks (Berardinelli, de Temino, Frattasi, Rahman, & Mogensen, 2008). In wireless environment, OFDMA shows robustness in the presence of multipath signal propagation by the parallel transmission of the information on M orthogonal and equally spaced subcarriers. However, on the other hand, OFDMA system exhibits an high envelop variation in its waveform which results an high peak to average power ratio (PAPR). Signals exhibiting high PAPR, require highly linear amplifiers to safeguard the system from intermodulation interference. This linearity is achieved if linear amplifiers at the transmitter operate with large back off from their peak power. This results in low power efficiency and if used for uplink transmission will put a significant burden on the portable wireless station (Fantacci, Marabissi, & Papini, 2004a). Another drawback of OFDMA is that it exhibits a certain offset in the frequency reference between the transmitter and receiver. This frequency offset can destroy the orthogonality of the transmission which introduces inter-carrier interference.
To overcome the above described drawbacks of OFDMA, the Third Generation Partnership Project (3GPP) introduced SC-FDMA for the uplink transmission which is a modified form of OFDMA (Rumney, 2008). As in OFDMA, SC-FDMA system transmit the information signals on different orthogonal frequency subcarriers. However, it transmits the subcarriers in sequence rather than in parallel which reduces the envelop fluctuation of waveform and results in low PAPR than OFDMA system (Ciochina, Castelain, Mottier, & Sari, 2009). In wireless environment with severe multipath, SC-FDMA signals arrive at the base station with inter-symbol interference. However, the base station employs adaptive frequency domain equalization to overcome this inter-symbol interference issue. In this way, the processing burden is shifted from the portable wireless station to the more powerful base station (Huang, Nix, & Armour, 2007; Lafuente-Martinez, Hernandez-Solana, Guio, & Valdovinos, 2011; Raghunath & Chockalingam, 2009). With the evolving wireless technologies, the demand of voice over IP, video conferencing, high data rate demanding wireless gaming, etc is also increasing (Falconer, Ariyavisitakul, Benyamin-Seeyar, & Eidson, 2002). Therefore, in wireless networks, intelligent and efficient resource allocation is very essential for meeting the demands of wireless users and achieving the goals of the service providers. Likewise any other wireless network, with the increasing wireless services, the multiple users in SC-FDMA uplink compete for the limited available radio spectrum. Secondly, the uplink systems are more vulnerable to energy losses as they are generally operated on the batteries with limited energy supply capabilities. Therefore, resource allocation with efficient spectrum utilization and optimized energy consumption is very important for uplink SC-FDMA systems.
Key Terms in this Chapter
PAPR: PAPR stands for Peak Average to Power Ratio. It is defined as the ratio of peak power to average power. It is a relationship between peak power and average power.
SC-FDMA: SC-FDMA is a single carrier frequency division multiple access technique. It is also known as linear pre-coded OFDMA because an extra block of DTFT is present in SC-FDMA.
CSI: In wireless communications, channel state information refers to known channel properties of a communication link. This information describes how a signal propagates from the transmitter to the receiver and represents the combined effect of signal.
OFDMA: OFDMA stands for orthogonal frequency division multiple access technique. In this technique, multiple users orthogonally access the channel simultaneously to avoid interference.
Distributed Resource Allocation: In distributed resource allocation, resource allocation decision are taken at user side.
QoS: Quality of service is the description of the overall performance of a service. It refers to any technology that manages data traffic to reduce packet loss, latency, and jitter on the network. QoS controls and manages network resources by setting priorities for specific types of data on the network.
Centralized Resource Allocation: In centralized resource allocation, first, a user reports its channel station information to the BS and then BS sends the resource allocation information to the user.