Introduction to Wireless Networking ECE/CSC 575 – Section 1 Introduction to Wireless Networking Lecture 1 Dr. Xinbing Wang

Current Wireless Systems: Cellular Systems--UMTS Fundamentals of cellular communications System capacity frequency reuse Cell splitting Admission control handoff Universal mobile telecommunication system (UMTS) Network architecture Functional units Quality of service Mobility management In our daily lives, wireless communication technology is used everywhere, from VCR remote control, to satellite weather forecast. The common characteristics of wireless communication systems is that there is no physical (visible) lines between two communication parties. Therefore, a wireless system is able to support user roaming. For example, we do not have to use a remote control in a particular position to.., we can use our cellular phones almost everywhere. However, there are many impairments to a wireless channel, causing a lot of limitations to wireless communications system such as geographical.. (signal fading, additional noise, cochannel interference. Wireless systems also suffers from limit usable spectral width, so that the transmission rate is relatively low. Specifically, wireless cellular systems based on radio propagation has been evolving from narrow band (1G, late 170s) to wide-band(3G). With their geographical coverage limitation, wireless systems need a backbone network to extend their geographical coverage to enable global communications. The interoworking of a wireless network as the front-end and the Internet as the backbone has received much attention in recent years. So we will first take a look at the network architecture of current wireless systems,…, Then we will talk about the evolution from 2G to 3G systems. Dr. Xinbing Wang

Node B Node B is the UMTS equivalent of a base station transceiver. It may support one or more cells, although in general only one cell one Node B. It is a logical terminal and the base station is often used for physical entity. Functions Mapping of Node B logical resources onto hardware resources Uplink power control Reporting of uplink interference measurements and downlink power information Contains the air interface physical layer, it has to perform many functions such as RF processing, modulations, coding, and so on. Dr. Xinbing Wang

Radio Network Controller (RNC) One RNC controls one or more Node Bs. It may be connected via Iu interface to an MSC (IuCS), or to an SGSN via Iu (IuPS). The interface between RNCs (Iur) is logical interface, and a direct physical connection does not necessarily exist. An RNC is comparable to a base station controller (BSC) in GSM networks. Dr. Xinbing Wang

RNC Functions Iub (Node B and RNC) transport resources management Control of Node B logical O&M resources System information management and scheduling Traffic management of common channels Soft handover Power control for uplink and downlink Admission control Traffic management of shared channels Macro diversity combining/splitting of data streams transferred over several Node Bs. Dr. Xinbing Wang

Admission Control In 2G TDMA systems In 3G CDMA systems The capacity in a TDMA cell is typically not interference limited, but it depends on the number of channel elements in the BS. It is easy to determine the amount of unused resources such as the number of free time slots Admission control is threshold-based In 3G CDMA systems A new call increases the overall interference level in the cells, and thus it has a direct effect on the QoS the other users in the cell Uplink: most of the interference is intracell, but intercell interference has to be considered as well. Downlink: orthogonal codes are used, and thus the capacity-limiting factor is mostly intercell interference Dr. Xinbing Wang

Admission Control (2) The admission-control algorithm must reside in the RNC, which has sole access to all the required information to run an efficient admission control policy. General idea Estimate the increase in the usage of resources the new user would cause If the estimation reveals that the new status would exceed the preset threshold, then the request for the resource has to be rejected When the total level in a cell is low, an increase to the load level increases the interference level only by a small amount, otherwise, it will cause a large increase in the interference level. Dr. Xinbing Wang

AC Procedure Determine the amount of available channels, i.e., the number of channels for accepting new and handoff requests. When the N-th request arrives, i.e., there are (N-1) ongoing services. If there are enough resources to admit the N-th request, then the new request is admitted. Otherwise, it will be denied. In order to maintain the continuity of a handoff call, handoff calls are given higher priority than new call requests. The prioritized call admission is implemented by reserving channels for handoff calls. This method is referred to as guard channels. Fixed reservation and dynamic reservation. Dr. Xinbing Wang

Examples of AC Admission control schemes are not specified in 3GPP technical specifications. Signaling procedures and measurements are needed to support admission control. Admission control algorithms are the internal functions of RNC, defined by the operator or by the equipment manufacturer. It is very difficult to discuss because some services have never been used before. The packet-level admission control is a new experience for mobile systems, which needs to consider the delay as a requirement whereas not equally evident for the wired networks. Dr. Xinbing Wang

Ex1: Interference-based AC Estimation of the increased interference level in uplink Interference Maximum allowed Interference level interference 2 load 2 load 1 load interference 1 Dr. Xinbing Wang

Layered Architecture There are three protocol layers in the AS Physical layer (L1) Data link layer (L2) Medium access control (MAC) Radio link control (RLC) Broadcast/multicast control (BMC) Packet data convergence protocol (PDCP) Network layer (L3) Radio resource control (RRC) There is one layer (L3) in the NAS Mobility management Call management Dr. Xinbing Wang

RLC Functions These functions (for itself) are supported by the RLC: Segmentation and reassembly of higher-layer PDUs (Protocol Data Unit) into/from smaller RLC payload units Padding Transfer of user data Error corrections In-sequence delivery of higher-layer PDUs Flow control Ciphering Sequence number check Dr. Xinbing Wang

RRC Functions These functions (for itself) are supported by the RRC: Initial cell selection and cell reselection Broadcast of information Reception of paging and notification messages Establishment, maintenance, and release of RRC connections Establishment, reconfiguration, and release of radio bearers Assignment, reconfiguration, and release of radio resources for the RRC connection Handover Measurement control Power control Security mode control QoS control Dr. Xinbing Wang

RRC Connection Procedures The UTRAN separates the concepts of a radio connection from a radio bearer (RB). A radio connection is created first, and then the network can create one or more RBs independently of the radio connection. An RB can also exist without a dedicated radio connection. In this case, the RB uses the common channels. An RRC connection implies that a radio connection exists, but this connection can use either dedicated or common resources. An RRC connection is a logical concept, and radio connection is a physical concept. The physical entity implements and enables the logical concepts. A dedicated connection allocates the resource exclusively to one user, so common channels should be used whenever possible. Dr. Xinbing Wang

RRC Establishment/Release RRC connection establishment It is always initiated by the UE, even with a mobile-terminated call (e.g.,paging). The UE initiates this procedure, but the UTRAN controls it. It may decide that no radio resources can be allocated for the UE, and respond with an RRC connection reject message. Signaling connection establishment The RRC connection establishment procedure is used by the higher layer; that is, by the NAS. All higher-layer signaling messages, including the initial messages are relayed through the radio interface. RRC connection release The normal procedure is finished through a dedicated channel (DCH). The PDU here are sent in unacknowledged mode. Dr. Xinbing Wang

Current Wireless Systems: Cellular Systems--UMTS Fundamentals of cellular communications System capacity frequency reuse Cell splitting Admission control handoff Universal mobile telecommunication system (UMTS) Network architecture Functional units Quality of service Mobility management In our daily lives, wireless communication technology is used everywhere, from VCR remote control, to satellite weather forecast. The common characteristics of wireless communication systems is that there is no physical (visible) lines between two communication parties. Therefore, a wireless system is able to support user roaming. For example, we do not have to use a remote control in a particular position to.., we can use our cellular phones almost everywhere. However, there are many impairments to a wireless channel, causing a lot of limitations to wireless communications system such as geographical.. (signal fading, additional noise, cochannel interference. Wireless systems also suffers from limit usable spectral width, so that the transmission rate is relatively low. Specifically, wireless cellular systems based on radio propagation has been evolving from narrow band (1G, late 170s) to wide-band(3G). With their geographical coverage limitation, wireless systems need a backbone network to extend their geographical coverage to enable global communications. The interoworking of a wireless network as the front-end and the Internet as the backbone has received much attention in recent years. So we will first take a look at the network architecture of current wireless systems,…, Then we will talk about the evolution from 2G to 3G systems. Dr. Xinbing Wang

Quality of Services Classes The UMTS allows the UEs to negotiate the QoS parameters for a radio bearer (RB). Negotiation The procedure is always initiated by the application in the UE. It sends a request defining the resources it needs The network checks whether it can provide the requested resources. It can either grant the requested resources, offer a small amount of resources, or reject the request. The UE can either accept or reject the modified offer. It is also possible to renegotiate these parameters if the application requirements change or resource status change. Dr. Xinbing Wang

QoS Classes (2) There are four types of QoS classes Conversational real-time class such as voice traffic Interactive class (best-effort) such as web browsing Streaming real-time class such as streaming video Background class (best-effort) such as emails. Dr. Xinbing Wang

Conversational Real-Time Services Bidirectional and more or less symmetric Technically the most challenging class Very short delay is acceptable Traditional retransmission protocols (ARQ) cannot be easily used. Instead, forward-error-correction (FEC) must be used. Small delay requirements means also that buffers cannot be used in receiving end to smooth the variations in delay (jitter). Some errors are acceptable because people cannot sense small errors in voice or video information. Dr. Xinbing Wang

Interactive Services A user requests data from a remote server, and the response contains the requested data. Web browsing, e-shopping, and database inquires. Difference between conversational and interactive services The data traffic in the conversational class is symmetric, whereas in the interactive class, the traffic is highly asymmetric. Timing requirements are not quite so strict with interactive services (up to 4 seconds) as they are for conversational services (a few hundred of ms). Interactive services do not tolerate any more transmission errors than conversational services. With the relaxation of delay requirements, the goal of less errors is easier to achieve with interactive services. Dr. Xinbing Wang

Streaming Services Typically includes video and audio applications. Differences from interactive services: The data transferring is almost totally one-way and continuous: highly asymmetric. There are some strict delay variation requirements for the data, which are presented to the user, whereas delay variation is not really a problem with interactive services. The requirements for maximum delay could be as long as 10 seconds. The only data traffic in the opposite direction ( usually in the uplink) consists of a few control signals like starting and stopping. The incoming data packets are buffered to smooth delay variation. This class is provided through packet-switched networks. Dr. Xinbing Wang

Background Services These services do not have precise delay requirements at all (fax and SMS). However, it may use timers to make sure that the data transfer has not stalled altogether. The data should be error free, but it is especially easy to achieve in this case. Because there are no time constraints. Retransmission protocol will be used, but it must also be efficient. Delay variation is not considered with background services. The data are presented to the user only after the whole file has been received correctly. The bandwidth requirement is not large in either direction. Dr. Xinbing Wang

Control of Requested QoS The UTRAN air interface is very flexible, which allows for the dynamic allocation of system resources. In the connected mode, the UE may be required to perform traffic volume measurements in its MAC layer. If the UE suspects that the present configuration is not the optimal one, it sends a measurement report to the network. The network can trigger a channel-reconfiguration procedure. Increased data Decreased data Dr. Xinbing Wang

UMTS Services (Originally) Data transmission service profile Circuit switched 16 kbit/s Voice SMS successor, E-Mail Packet switched 14.4 kbit/s Simple Messaging Switched Data asymmetrical, MM, downloads 384 kbit/s Medium MM Low coverage, max. 6 km/h 2 Mbit/s High MM Bidirectional, video telephone 128 kbit/s High Interactive MM Transport mode Bandwidth Service Profile Dr. Xinbing Wang

Current Wireless Systems: Cellular Systems--UMTS Fundamentals of cellular communications System capacity frequency reuse Cell splitting Admission control handoff Universal mobile telecommunication system (UMTS) Network architecture Functional units Quality of service Mobility management In our daily lives, wireless communication technology is used everywhere, from VCR remote control, to satellite weather forecast. The common characteristics of wireless communication systems is that there is no physical (visible) lines between two communication parties. Therefore, a wireless system is able to support user roaming. For example, we do not have to use a remote control in a particular position to.., we can use our cellular phones almost everywhere. However, there are many impairments to a wireless channel, causing a lot of limitations to wireless communications system such as geographical.. (signal fading, additional noise, cochannel interference. Wireless systems also suffers from limit usable spectral width, so that the transmission rate is relatively low. Specifically, wireless cellular systems based on radio propagation has been evolving from narrow band (1G, late 170s) to wide-band(3G). With their geographical coverage limitation, wireless systems need a backbone network to extend their geographical coverage to enable global communications. The interoworking of a wireless network as the front-end and the Internet as the backbone has received much attention in recent years. So we will first take a look at the network architecture of current wireless systems,…, Then we will talk about the evolution from 2G to 3G systems. Dr. Xinbing Wang

Mobility Management Why mobility management? To keep ongoing connections when users move in/out cells To update mobile users locations in the home network for service delivery What is mobility management? Location management: to “locate” mobile users within a location area and to “update” home location register (HLR). Handoff management: to “handoff” connections from one base station (BS) to another. Dr. Xinbing Wang

Location Management Location registration: Mobile users register with a new MSC when they move out of a region controlled by an old MSC. The mobile users register with a local/regional register, namely, visitor location register (VLR) in the visiting network. The mobile users then update their locations in terms of location area (LA) in the home location register (HLR) We assume one MSC is related to one or more LAs. And one MSC is collocated with one VLR. Dr. Xinbing Wang

Two-Tier Architecture The first tier is centered on HLR and SS7. The second tier is featured by VLRs and MSCs. HLR SS7 Home Location Register (HLR) Mobile Switching Center (MSC) Visitor Location Register (VLR) MSC VLR VLR MSC Location area (LA) Cell Dr. Xinbing Wang

After Class Reading materials Exercises Reading materials for UMTS Reading materials reserved for book “Introduction to 3G Mobile Communications.” Exercises List 3 functions of RLC and RNC, respectively What is admission control? In which entity AC is implemented? Explain the procedure of admission control Explain the interference-based scheme in the lecture notes. Can you think of two other schemes? What are the Quality of Service classes in UMTS? How are they classified? What is objective of mobility management? Explain the functions of HLR/VLR/MSC. Dr. Xinbing Wang