A secondary telecommunications channel that resides within the main channel (a carrier within a carrier). A type of multiplexing, the subcarrier is a modulated carrier signal at a lower frequency that is combined with the main carrier signal running at a higher frequency.
Many Uses
Color TV signals were added in a subcarrier to black and white signals in order to maintain backward compatibility with monochrome TV sets. Stereo was added to FM radio in a subcarrier for compatibility. Subcarriers are also often used to provide the audio channel in a video broadcast. See carrier.
Many Uses
Color TV signals were added in a subcarrier to black and white signals in order to maintain backward compatibility with monochrome TV sets. Stereo was added to FM radio in a subcarrier for compatibility. Subcarriers are also often used to provide the audio channel in a video broadcast. See carrier.
 | Reproduced with permission from Computer Desktop Encyclopedia. Copyright (c) 1981-2008 The Computer Language Company Inc. All rights reserved. |
Additional Resources
- Optimal Scheduling for OFDMA Systems
- This paper considers a scheduling and resource allocation problem for the downlink of an OFDMA-based wireless network, where the channel estimation error is modeled by a self-noise term in the decoding process. During each time-slot this involves selecting a subset of users for transmission, determining the assignment of available subcarriers...
- White papers 2006-11-24
- Adaptive OFDM Techniques With One-Bit-Per-Subcarrier Channel-State Feedback
- In the Orthogonal Frequency-Division Multiplexing OFDM scheme, some subcarriers may be subject to a deep fading. Adaptive techniques can be applied to mitigate this effect if the Channel-State Information CSI is available at the transmitter. This paper studies the performance of an OFDM-based communication system whose transmitter has only one...
- White papers 2006-11-01
- Linear Precoding for Multiuser MIMO-OFDM Systems
- This paper develops linear precoding schemes for the downlink in multiuser Multiple-Input Multiple-Output MIMO Orthogonal Frequency Division Multiplexing OFDM systems with multiple data streams per user. The authors extend an existing multiuser MIMO algorithm, that jointly optimizes the power allocation and the transmit and receive filters, to MIMOOFDM systems. One...
- White papers 2006-09-28
- Delay Analysis and Comparison of OFDM-TDMA and OFDMA Under IEEE 802.16 QoS Framework
- The delay analysis and comparison of OFDM-TDMA and OFDMA using a flow control scheme under the QoS framework of IEEE 802.16 are conducted in the work discussed in this paper. The paper investigates the maximum packet delay performance by deriving delay bounds for several multiaccess modes with different subcarrier/time-slot assignment...
- White papers 2006-07-22
- Multichannel Feedback in OFDM Ad Hoc Networks
- This paper proposes a multichannel feedback protocol to enable local scheduling with channel state information for wireless networks with Orthogonal Frequency Division Multiplexing OFDM. In the proposed protocol, the frequency subcarrier domain is shared by multiple control channels, on which Request-To-Send RTS and Clear-To-Send CTS are exchanged. These control channels...
- White papers 2006-05-16
- On the Use of Adaptive Loading Algorithms in MIMO-OFDM Systems
- In this paper, Optimum adaptive loading algorithms are applied to Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing MIMOOFDM system. Chaw's and Compello's algorithms have been implemented to obtain a bit and power allocation for each subcarrier assuming instantaneous channel knowledge. Channel matrix Singular Value Decomposition SVD method has been employed in...
- White papers 2006-04-19
- Recursive and Trellis-Based Feedback Reduction for MIMO-OFDM With Rate-Limited Feedback
- This paper investigates an adaptive MIMO-OFDM system with a feedback link that can only convey a finite number of bits. This paper considers three different transmitter configurations; beamforming applied per OFDM subcarrier; precoded spatial multiplexing applied per subcarrier; and precoded orthogonal space time block coding applied per subcarrier. Depending on...
- White papers 2006-03-16
- Downlink Scheduling and Resource Allocation for OFDM Systems
- This paper considers scheduling and resource allocation for the downlink of a OFDM-based wireless network. During each time-slot the scheduling and resource allocation problem involves selecting a subset of users for transmission, determining the assignment of available subcarriers to selected users, and for each subcarrier determining the transmission power and...
- White papers 2006-02-27
- Performance Analysis of a Reuse Partitioning Technique for OFDM Based Evolved UTRA
- The current 3GPP working assumption on the Evolved Universal Terrestrial Radio Access (E-UTRA) physical layer is that it will be based on Single Carrier Frequency Division Multiple Access (SC-FDMA) for the uplink and Orthogonal Frequency Division Multiple Access OFDMA for the downlink. According to the concept specification, inter-cell interference mitigation...
- White papers 2006-02-01
- Resource Allocation in OFDMA Wireless Networks With Time-Varying Arrivals
- This paper considers the issue of optimal subcarrier allocation in OFDMA wireless networks when the arrivals and channels are stochastic and time-varying. The objective is to minimize the long-term average packet delay over multiple time epochs. This paper shows by example that water-filling-based subcarrier allocation policy which maximizes throughput at...
- White papers 2005-11-14
- Interpolation Based Transmit Beamforming for MIMO-OFDM With Limited Feedback
- Transmit beamforming and receive combining are simple methods for exploiting spatial diversity in Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system. Optimal beamforming requires channel state information in the form of the beamforming vectors for each OFDM subcarrier. This paper proposes to a limited feedback architecture that combines beamforming vector...
- White papers 2005-11-11
- Joint Allocation of Subcarriers and Transmit Powers in a Multiuser OFDM Cellular Network
- This paper considers the problem of joint bandwidth subcarriers and power allocation for the downlink of a multi-user multi-cell OFDM cellular network. This resource allocation problem is formulated as a power minimization problem, subject to meeting the target rates of all users in the network. The authors develop a distributed...
- White papers 2005-09-23
- Energy-Efficient MAC-PHY Resource Management With Guaranteed QoS in Wireless OFDM Networks
- Most of the current resource management algorithms are confined to a single layer of the network protocol stack, which leads to an inferior system performance. This paper proposes a joint MAC-PHY layer resource allocation algorithm. The proposed algorithm jointly optimizes the bandwidth and power allocation through an integrated design of...
- White papers 2005-08-09
- Quantized Multi-Mode Precoding for Spatial Multiplexing MIMO-OFDM Systems
- Spatial multiplexing with multi-mode precoding can achieve both high capacity and high reliability in Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) systems. Multimode precoding uses linear transmit precoding but adapts the number of transmit streams or modes according to the channel conditions. Multi-mode precoding typically requires complete knowledge of the transmit...
- White papers 2005-06-25
- Slow Subcarrier-Hopped Space Division Multiple Access OFDM Systems
- Space Division Multiple Access SDMA assisted Multi-Input-Multi-Output MIMO OFDM systems invoking Multi-User Detection MUD techniques have attracted substantial research interests, which are capable of exploiting both transmitter multiplexing gain and receiver diversity gain. Furthermore, the classic Frequency-Hopping FH technique can be effectively amalgamated with SDMA-OFDM systems, resulting in Frequency-Hopped FH...
- White papers 2005-03-18
- Adaptive Scheduling for Heterogeneous Traffic Flows in Cellular Wireless OFDM-FDMA Systems
- This paper studies the performance gain achieved by introducing dynamic subcarrier scheduling schemes to OFDM systems in the presence of heterogeneous traffic streams. Dynamic subcarrier scheduling copes with channel state variation by dynamically assigning different subcarriers to terminals, e.g. in the downlink of a cellular system. In addition to the...
- White papers 2005-03-11
- Cross-Layer Optimization for OFDM Wireless Networks - Part II: Algorithm Development
- The authors have established a theoretical framework for cross-layer optimization in Orthogonal Frequency Division Multiplexing OFDM wireless networks. This paper focuses on effective and practical algorithms for efficient and fair resource allocation in OFDM wireless networks. The authors have taken various conditions into account and developed a variety of efficient...
- White papers 2005-03-01
- Interpolation-Based Multi-Mode Precoding for MIMO-OFDM Systems
- Spatial multiplexing with multi-mode precoding provides a means to achieve both high capacity and high reliability in Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) systems. Multi-mode precoding uses linear transmit precoding that adapts the number of spatial multiplexing data streams or modes, according to the transmit Channel State Information CSI....
- White papers 2005-02-09
- Rate Stable Resource Allocation in OFDM Systems: From Water-Filling to Queue-Balancing
- This paper considers the issue of optimal subcarrier allocation in OFDMA. The authors show, via a counter example, that water-filling based subcarrier allocation policies, contrary to conventional wisdom, fail to provide rate-stability for an otherwise stabilizable OFDMA system. Water-filling is too myopic when considering longtime average performance, e.g. delay, queue...
- White papers 2004-12-05
- A Fresh Look at Optimal Subcarrier Allocation in OFDMA Systems
- This paper considers the issue of optimal subcarrier allocation in OFDMA. This paper shows, via a counter example, that water-filling based subcarrier allocation policies, contrary to conventional wisdom, fail to provide rate-stability for an otherwise stabilizable OFDMA system. Water-filling is too myopic when considering long-time average performance, e.g. delay, queue...
- White papers 2004-09-09
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