Dynamic single-frequency networks
Encyclopedia
Dynamic Single Frequency Networks (DSFN) is a transmitter macrodiversity
technique for OFDM based cellular networks.
DSFN is based on the idea of single frequency networks (SFN), which is a group of radio transmitters that send the same signal simultaneously over the same frequency. The term originates from the broadcasting world, where a broadcast network
is a group of transmitters that send the same TV or radio program. Digital wireless communication systems based on the OFDM modulation scheme are well-suited to SFN operation, since OFDM in combination with some forward error correction scheme can eliminate intersymbol interference
and fading
caused by multipath propagation without the use of complex equalization
.
The concept of DSFN implies the SFN grouping is changed dynamically over time, from timeslot to timeslot. The aim is to achieve efficient spectrum utilization for downlink unicast
or multicast
communication services in centrally controlled cellular systems based on for example the OFDM modulation scheme. A centralized scheduling algorithm
assigns each data packet to a certain timeslot, frequency channel and group of base station transmitters. DSFN can be considered as a combination of packet scheduling, macro-diversity and dynamic channel allocation (DCA). The scheduling algorithm can be further extended to dynamically assign other radio resource management
parameters to each timeslot and transmitter, such as modulation scheme and error correction scheme, in view to optimize the efficiency.
DSFN makes it possible to increase the received signal strength to a mobile terminal in between several base station transmitters in comparison to non-macrodiversity communication schemes. Thus, DSFN can improve the coverage area and lessen the outage probability. Alternatively, DSFN may allow the same outage probability with a less robust but more efficient modulation
and error coding scheme, and thus improve the spectral efficiency
in bit/s/Hz/base station transmitter in comparison to a non-macrodiversity communication scheme.
DSFN resembles the CDMA downlink soft handover
. A difference is that in the CDMA case, co-channel interference from transmissions to other users are more efficiently avoided by giving the other users other spreading codes.
A special form of DSFN is Continuous Transmission DSFN, where all base station transmitters always transmit at full power, without blocking of non-utilized transmitters, and without power control. This concept is very similar to so called Virtual cellular networks (VCNs), where a virtual cell is a group of base stations sending using the same spreading code, or a group of OFDM transmitters form a Single Frequency Network.
DSFN schemes can be described as a form of "virtual" power control.
Macrodiversity
In the field of wireless communication, Macrodiversity is a kind of space diversity scheme using several receiver antennas and/or transmitter antennas for transferring the same signal...
technique for OFDM based cellular networks.
DSFN is based on the idea of single frequency networks (SFN), which is a group of radio transmitters that send the same signal simultaneously over the same frequency. The term originates from the broadcasting world, where a broadcast network
Broadcast network
A broadcast network is an organization, such as a corporation or other voluntary association, that provides live television or recorded content, such as movies, newscasts, sports, Public affairs programming, and other television programs for broadcast over a group of radio stations or television...
is a group of transmitters that send the same TV or radio program. Digital wireless communication systems based on the OFDM modulation scheme are well-suited to SFN operation, since OFDM in combination with some forward error correction scheme can eliminate intersymbol interference
Intersymbol interference
In telecommunication, intersymbol interference is a form of distortion of a signal in which one symbol interferes with subsequent symbols. This is an unwanted phenomenon as the previous symbols have similar effect as noise, thus making the communication less reliable...
and fading
Fading
In wireless communications, fading is deviation of the attenuation that a carrier-modulated telecommunication signal experiences over certain propagation media. The fading may vary with time, geographical position and/or radio frequency, and is often modelled as a random process. A fading channel...
caused by multipath propagation without the use of complex equalization
Equalization
Equalization, is the process of adjusting the balance between frequency components within an electronic signal. The most well known use of equalization is in sound recording and reproduction but there are many other applications in electronics and telecommunications. The circuit or equipment used...
.
The concept of DSFN implies the SFN grouping is changed dynamically over time, from timeslot to timeslot. The aim is to achieve efficient spectrum utilization for downlink unicast
Unicast
right|200pxIn computer networking, unicast transmission is the sending of messages to a single network destination identified by a unique address.-Addressing methodologies:...
or multicast
Multicast
In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires...
communication services in centrally controlled cellular systems based on for example the OFDM modulation scheme. A centralized scheduling algorithm
Algorithm
In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...
assigns each data packet to a certain timeslot, frequency channel and group of base station transmitters. DSFN can be considered as a combination of packet scheduling, macro-diversity and dynamic channel allocation (DCA). The scheduling algorithm can be further extended to dynamically assign other radio resource management
Radio resource management
Radio resource management is the system level control of co-channel interference and other radio transmission characteristics in wireless communication systems, for example cellular networks, wireless networks and broadcasting systems...
parameters to each timeslot and transmitter, such as modulation scheme and error correction scheme, in view to optimize the efficiency.
DSFN makes it possible to increase the received signal strength to a mobile terminal in between several base station transmitters in comparison to non-macrodiversity communication schemes. Thus, DSFN can improve the coverage area and lessen the outage probability. Alternatively, DSFN may allow the same outage probability with a less robust but more efficient modulation
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
and error coding scheme, and thus improve the spectral efficiency
Spectral efficiency
Spectral efficiency, spectrum efficiency or bandwidth efficiency refers to the information rate that can be transmitted over a given bandwidth in a specific communication system...
in bit/s/Hz/base station transmitter in comparison to a non-macrodiversity communication scheme.
DSFN resembles the CDMA downlink soft handover
Soft handover
Soft handover or soft handoff refers to a feature used by the CDMA and WCDMA standards, where a cell phone is simultaneously connected to two or more cells during a call. If the sectors are from the same physical cell site , it is referred to as softer handoff...
. A difference is that in the CDMA case, co-channel interference from transmissions to other users are more efficiently avoided by giving the other users other spreading codes.
A special form of DSFN is Continuous Transmission DSFN, where all base station transmitters always transmit at full power, without blocking of non-utilized transmitters, and without power control. This concept is very similar to so called Virtual cellular networks (VCNs), where a virtual cell is a group of base stations sending using the same spreading code, or a group of OFDM transmitters form a Single Frequency Network.
DSFN schemes can be described as a form of "virtual" power control.
See also
- Antenna diversityAntenna diversityAntenna diversity, also known as space diversity, is any one of several wireless diversity schemes that uses two or more antennas to improve the quality and reliability of a wireless link. Often, especially in urban and indoor environments, there is no clear line-of-sight between transmitter and...
- Cooperative diversityCooperative diversityCooperative diversity is a cooperative multiple antenna technique for improving or maximising total network channel capacities for any given set of bandwidths which exploits user diversity by decoding the combined signal of the relayed signal and the direct signal in wireless multihop networks...
- Macro diversity
- OFDM
- Single Frequency Networks (SFN)