Hierarchical modulation: Difference between revisions
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Broadcast multicast service (BCMCS) has increasingly been popular for delivering multimedia content to mobile users. Traditional digital broadcast air interfaces are designed with the tradeoff between maximum achievable rate and intended coverage in mind. The actual rates are usually limited by the maximum transmit power and the worst channel condition so that every user in coverage can reliably receive the services as well as contents of same quality. The users under good reception condition may have no advantage, even if their potential throughputs can be much higher. This happens often, especially on the mobile users whose reception conditions change all the time. And there are rising interests in upgrading existing digital broadcast systems with more services for new users and delivering more quality of service (QoS) options to users with advanced receivers while still guaranteeing existing users' services. Furthermore, recent advances in wideband speech coding, e.g., EVRC-WB, and scalable video coding, e.g., H.264/MPEG-4 AVC, suggest unequal error protection on content delieveries with providing graceful degradation of quality in the presence of increasing packet loss. It is possible for the users in good reception condition have more opportunities to enjoy high quality services while the user with low throughput can still decode the content of basic quality. Many technologies are under investigation for these goals, e.g., rateless coding, hierarchical modulation, multiple-input multiple-output (MIMO), selective retransmission and superposition precoding (SPC). Backward compatibility, implementation complexity and upgrading cost are among the major concerns in upgrading existing systems with additional services. Among those candidates, hierarchical modulation, also called layered modulation, is the most popular one, in which multiple data streams are multiplexed and modulated into one single symbol consisting of base-layer subsymbols and enhancement-layer subsymbols. It has been widely proven and included in various standards, such as DVB-T, MediaFLO, UMB (Ultra Mobile Broadband, a new 3.5th generation mobile network standard developed by 3GPP2), etc., and is under study for DVB-H. |
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'''Hierarchical modulation''', also called '''layered modulation''', is one of the [[signal processing]] techniques for [[multiplexing]] and [[modulation|modulating]] multiple data streams into one single symbol stream, where base-layer symbols and enhancement-layer symbols are synchronously overplayed to together before transmission. |
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Hierarchical modulation has been widely proven and included in various standards, such as [[DVB-T]], [[MediaFLO]], UMB ([[Ultra Mobile Broadband]], a new 3.5th generation mobile network standard developed by 3GPP2), and is under study for [[DVB-H]]. |
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Hierarchical modulation, also called layered modulation, is one of the signal processing techniques for multiplexing and modulating multiple data streams into one single symbol stream, where base-layer symbols and enhancement-layer symbols are synchronously overplayed to together before transmission. Hierarchical modulation is also taken as one of the practical implementation of superposition precoding, which can help achieve the maximum sum rate of broadcast channels. When hierarchical-modulated signals are transmitted, users with good reception and advanced receiver can demodulate multiple layers. For a user with conventional receiver or poor reception condition, it may only demodulate the data stream embedded in the base layer. With hierarchical modulation, a network operator can target users of different types with different services or QoS's. However, traditional hierarchical modulation suffers from serious inter-layer interference (ILI) so that the achievable rate by low-layer data stream, e.g. the base-layer data stream, is dented by the interference from high-layer signal(s). For example, for a hierarchically modulated symbol with 16QAM base layer and QPSK enhancement layer, the base-layer throughput loss is up to about 1.5bits/symbol with the total receive signal-to-noise ratio (SNR) at about 23 dB, which is necessary for taking the full potentials of 64-ary QAM. This means, due to ILI, about 1.5/4 = 37.5% loss of the base-layer achievable throughput. Furthermore, due to ILI and the imperfect demodulation of base-layer symbols, the demodulation error rate of higher-layer symbols increases too. |
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Hierarchical modulation is also taken as one of the practical implementation of superposition precoding, which can help achieve the maximum sum rate of broadcast channels. When hierarchical-modulated signals are transmitted, users with good reception and advanced receiver can demodulate multiple layers. For a user with conventional receiver or poor reception condition, it may only demodulate the data stream embedded in the base layer. With hierarchical modulation, a network operator can target users of different types with different services or QoS's. |
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However, traditional hierarchical modulation suffers from serious inter-layer interference (ILI) so that the achievable rate by low-layer data stream, e.g. the base-layer data stream, is dented by the interference from high-layer signal(s). |
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For example, for a hierarchically modulated symbol with 16QAM base layer and QPSK enhancement layer, the base-layer throughput loss is up to about 1.5bits/symbol with the total receive signal-to-noise ratio (SNR) at about 23 dB, which is necessary for taking the full potentials of 64-ary QAM. This means, due to ILI, about 1.5/4 = 37.5% loss of the base-layer achievable throughput. Furthermore, due to ILI and the imperfect demodulation of base-layer symbols, the demodulation error rate of higher-layer symbols increases too. |
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==See also== |
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* [[Link adaptation]] |
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==External links== |
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*[http://www.broadcastpapers.com/whitepapers/paper_loader.cfm?pid=520 Hierarchical Modulation Explained] |
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*[http://www.dvb.org/technology/fact_sheets/WP01_DVB-T%20Hierarchical.pdf Hierarchical Modulation under DVB] |
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[[Category:Radio modulation modes]] |
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[[Category:Radio resource management]] |
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Revision as of 08:35, 16 June 2008
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Hierarchical modulation, also called layered modulation, is one of the signal processing techniques for multiplexing and modulating multiple data streams into one single symbol stream, where base-layer symbols and enhancement-layer symbols are synchronously overplayed to together before transmission.
Hierarchical modulation has been widely proven and included in various standards, such as DVB-T, MediaFLO, UMB (Ultra Mobile Broadband, a new 3.5th generation mobile network standard developed by 3GPP2), and is under study for DVB-H.
Hierarchical modulation is also taken as one of the practical implementation of superposition precoding, which can help achieve the maximum sum rate of broadcast channels. When hierarchical-modulated signals are transmitted, users with good reception and advanced receiver can demodulate multiple layers. For a user with conventional receiver or poor reception condition, it may only demodulate the data stream embedded in the base layer. With hierarchical modulation, a network operator can target users of different types with different services or QoS's.
However, traditional hierarchical modulation suffers from serious inter-layer interference (ILI) so that the achievable rate by low-layer data stream, e.g. the base-layer data stream, is dented by the interference from high-layer signal(s).
For example, for a hierarchically modulated symbol with 16QAM base layer and QPSK enhancement layer, the base-layer throughput loss is up to about 1.5bits/symbol with the total receive signal-to-noise ratio (SNR) at about 23 dB, which is necessary for taking the full potentials of 64-ary QAM. This means, due to ILI, about 1.5/4 = 37.5% loss of the base-layer achievable throughput. Furthermore, due to ILI and the imperfect demodulation of base-layer symbols, the demodulation error rate of higher-layer symbols increases too.