Wireless Communications

A cellular base station serves a multiplicity of single-antenna terminals over the same time-frequency interval. Time-division duplex operation combined with reverse-link pilots enables the base station to estimate the reciprocal forward- and reverse-link channels. The conjugate-transpose of the channel estimates are used as a linear precoder and combiner respectively on the forward and reverse links. Propagation, unknown to both terminals and base station, comprises fast fading, log-normal shadow fading, and geometric attenuation. In the limit of an infinite number of antennas a complete multi-cellular analysis, which accounts for inter-cellular interference and the overhead and errors associated with channel-state information, yields a number of mathematically exact conclusions and points to a desirable direction towards which cellular wireless could evolve. In particular the effects of uncorrelated noise and fast fading vanish, throughput and the number of terminals are independent of the size of the cells, spectral efficiency is independent of bandwidth, and the required transmitted energy per bit vanishes. The only remaining impairment is inter-cellular interference caused by re-use of the pilot sequences in other cells (pilot contamination) which does not vanish with unlimited number of antennas.

Noncooperative Cellular Wireless with Unlimited Numbers of Base Station Antennas

Multiple-input multiple-output (MIMO) technology is maturing and is being incorporated into emerging wireless broadband standards like long-term evolution (LTE) [1]. For example, the LTE standard allows for up to eight antenna ports at the base station. Basically, the more antennas the transmitter/receiver is equipped with, and the more degrees of freedom that the propagation channel can provide, the better the performance in terms of data rate or link reliability. More precisely, on a quasi static channel where a code word spans across only one time and frequency coherence interval, the reliability of a point-to-point MIMO link scales according to Prob(link outage) ` SNR-ntnr where nt and nr are the numbers of transmit and receive antennas, respectively, and signal-to-noise ratio is denoted by SNR. On a channel that varies rapidly as a function of time and frequency, and where circumstances permit coding across many channel coherence intervals, the achievable rate scales as min(nt, nr) log(1 + SNR). The gains in multiuser systems are even more impressive, because such systems offer the possibility to transmit simultaneously to several users and the flexibility to select what users to schedule for reception at any given point in time [2].

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Scaling Up MIMO: Opportunities and Challenges with Very Large Arrays

The quintessential goal of sensor array signal processing is the estimation of parameters by fusing temporal and spatial information, captured via sampling a wavefield with a set of judiciously placed antenna sensors. The wavefield is assumed to be generated by a finite number of emitters, and contains information about signal parameters characterizing the emitters. A review of the area of array processing is given. The focus is on parameter estimation methods, and many relevant problems are only briefly mentioned. We emphasize the relatively more recent subspace-based methods in relation to beamforming. The article consists of background material and of the basic problem formulation. Then we introduce spectral-based algorithmic solutions to the signal parameter estimation problem. We contrast these suboptimal solutions to parametric methods. Techniques derived from maximum likelihood principles as well as geometric arguments are covered. Later, a number of more specialized research topics are briefly reviewed. Then, we look at a number of real-world problems for which sensor array processing methods have been applied. We also include an example with real experimental data involving closely spaced emitters and highly correlated signals, as well as a manufacturing application example.

Two decades of array signal processing research: the parametric approach

It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

This chapter highlights some of the driving forces behind the 3G evolution, giving the reader an understanding of where the technical requirements and solutions are coming from. A key factor for success in any business is to understand the forces that will drive the business in the future. This is in particular true for the mobile-communication industry. Here the rapid growth of the number of subscribers and the global presence of the technologies have attracted several new players that want to be successful. The chapter also discusses Radio Access Network (RAN) approaches and an evolved core network with regard to the 3G evolution, In addition to Long-Term Evolution (LTE) and high-speed packet access (HSPA).An evolved core network, the “Evolved Packet Core,” was developed to ensure that an operator can coexist easily between HSPA Evolution and LTE. The System Architecture Evolution (SAE) study focused on how the 3GPP core network will evolve into the core network of the next decades. The philosophy of the SAE is to focus on the packet-switched domain and migrate away from the circuit-switched domain. This is done through the coming 3GPP releases ending up with the Evolved Packet Core.

The motives behind the 3G evolution

Publisher Summary
This chapter presents an overview of the multimedia broadcast/multicast services (MBMS). The MBMS support multicast/broadcast services in a cellular system, thereby combining the provision of multicast/broadcast and unicast services within a single network. With MBMS, the same content is transmitted to multiple users located in a specific area, known as the MBMS service area and typically comprising multiple cells. In each cell participating in the transmission, a point-to-multipoint radio resource is configured, and all users subscribing to the MBMS service simultaneously receive the same transmitted signal. No tracking of users' movement in the radio-access network is performed, and users can receive the content without notifying the network. When providing multicast/broadcast services for mobile devices, there are several aspects to take into account, of which two most important issues include good coverage and low terminal power consumption. This chapter begins with discussing the architecture of MBMS single-frequency network (MBSFN) area. Overall channel structure and physical layer processing is also discussed. The chapter concludes with a discussion on scheduling of MBMS services.

Chapter 15 – Multimedia Broadcast/Multicast Services

This chapter discusses the architecture of Long-Term Evolution (LTE) radio interface. It describes the various LTE protocol structure, including Radio Link Control (RLC), Medium Access Control (MAC), and the physical layer, explaining the logical and physical channels, the related procedures, and data flows. The processing specified for LTE is structured into different protocol layers. This chapter contains a description of the protocol layers above the physical layer, their interaction, and the interface to the physical layer. RLC is responsible for segmentation/concatenation, retransmission handling, and in-sequence delivery to higher layers. The RLC offers services to the Packet Data Convergence Protocol (PDCP) in the form of radio bearers. Furthermore, MAC handles hybrid-automatic repeat request (ARQ) retransmissions and uplink and downlink scheduling. The scheduling functionality is located in the eNodeB, which has one MAC entity per cell, for both uplink and downlink. The hybrid-ARQ protocol part is present in both the transmitting and receiving end of the MAC protocol. The MAC offers services to the RLC in the form of logical channels..

LTE radio interface architecture

In a cellular system (100), transmissions are made (410) in subframes (310) which comprise subelements. The method is used for scheduling (415) first and second channels in a subframe, and comprises: • dividing (420) the transmission resources for the first channel into a first set of resource groups, • assigning (425) the resource groups of the first set to subelements in the subframe (310) in a predetermined fashion, • assigning (430) a symbol value to all subelements (210) in the subframe (310) which have not been assigned a resource groups of the first set, • dividing (435) the transmission resources for the second channel into a second set of resource groups, • assigning (440) the resource groups of the second set to subelements in the subframe by means of said symbol values.

Improved scheduling in a cellular system

There are provided mechanisms for monitoring search spaces. A first method performed by a wireless device comprises receiving an OFDM symbol in a downlink slot. At least part of the OFDM symbol is included in a device-specific search space and in a common search space. The first method comprises monitoring the device-specific search space for at least one device-specific reference signal (RS) and monitoring the common search space for at least one non-device-specific RS. In a second method, a radio access network node transmits an OFDM symbol included in a device-specific search space and in a common search space. The device-specific search space contains a device-specific RS, or the non-device specific search space contains a non-device-specific RS, or both of these apply.

Stefan Parkvall

Papers

The motives behind the 3G evolution

Chapter 15 – Multimedia Broadcast/Multicast Services

LTE radio interface architecture

Improved scheduling in a cellular system

Search space monitoring in wireless communication networks