Wireless Systems Integration Through MAC Jahangir Dadkhah Chimeh Islamic Azad University Science and Research Branch
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Seyed Mohammadreza Hashemiannejad
Abstract Today wireless Internet communications are very attractive. Although many systems can provide user access to the Internet, but they have different air interfaces, backbone and data bases. To save network resources and investments we should use a unique resource for whole the network. In this paper we pay attention to three different wireless systems, UMTS, WLAN, WiMax and integration methods, then suggest a new integration method by the new Base Station Bridge which operates in the layer two/MAC. Keywords: Integration, Wireless system, Base Station Bridge, MAC.
1. Introduction UMTS, WLAN and WiMax can be connected to Internet. UMTS is capable to handle the real-time services as well as non-real-time services. WLAN and WiMax have been designed for high data rate transmissions, but can not handle real-time services well. Access methods are different in these systems. Access part includes layer one and some parts of layer two. Hu in [1] has suggested system integration in the BTS unit, i.e., an integration in layer one in which realization is quite difficult. Niyto and Hossain in [2] have only mentioned integration in layers 2 & 3 shortly but not in detail. Here, they have selected protocol adaptation in layer 3 because it didn’t need changes in hardware and software sections of WiFi users and WiMax BS. We know WLAN and WiMax use OFDM and UMTS uses WCDMA [3]. To remove the integration problems in layer one, we pay attention to integrating the systems in layer two. The data link layer is Layer 2 of the seven-layer OSI model as well as of the fivelayer TCP/IP reference model. It responds to service requests from the network layer and issues service requests to the physical layer. The data link layer is split into MAC and LLC sub-layers. The uppermost
Mobile Communication Company of Iran
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sub-layer is the Logical Link Control (LLC). This sublayer provides functions such as segmentation/ reassembly, concatenation, padding, flow control. It also provides transparent data services, unacknowledged data transfer services, acknowledged data transfer services to the upper layer. Media Access Control (MAC) is below LLC. This refers to the sub-layer that determines who is allowed to access the media at any time (e.g. CSMA/CD or CSMA/CA). The Media Access Control sub-layer also determines where a frame of the data ends and the next frame starts. Thus in section 2 of this paper we study wireless system characteristics, introduce an architecture for the network integration in section three and make the conclusion in the end.
2. Wireless systems characteristics
parameters
and
UMTS is based on the 3GPP standards. UMTS users may have high mobility. After UMTS R99, releases 4-8 of UMTS can support higher data rates. A new air interface by the name of High Speed Packet Access (HSPA), supporting 1Mbps data rates for the mobile users, began from R4. In R4, UMTS introduced some new packet services and in R5, IP was used the only protocol in the core network [4]. UMTS R6 can support 14.4Mbps and 5.76Mbps data rates for downlink and uplink respectively. UMTS R7 and R8 evolved to UMTS Long Term Evolution (LTE) which improved some other QoS parameters, in addition to improving the data rate. These two revisions are also based on the Internet protocol entirely. UMTS LTE access method in the uplink and downlink are SCFDMA and OFDMA respectively [5]. - WLAN is based on IEEE 802.11 standard. WLAN includes access point (AP) and equipment users which may be fixed and portable [6], [7]. Table 1 lists its various standards.
Table 1. WLAN characteristics [6] Parameters 802.11b 802.11g Maximum 11Mbps 54Mbps Data rate Carrier 2.4GHz 2.4GHz Frequency CDMA / Modulation / OFDMA CCK, Coding HR/DSSS
802.11a 54Mbps 5GHz OFDA
- Identification of UEs on common transport channels; - Multiplexing/de-multiplexing of upper layer PDUs into/from frames delivered to/from the physical layer on common transport channels; - Multiplexing/de-multiplexing of upper layer PDUs into/from frames delivered to/from the physical layer on dedicated transport channels; - Segmentation and reassembly of upper layer PDUs. SAP
- WiMax is based on IEEE 802.16 standard. Since 2001 WiMAX has evolved from 802.16 to 802.16d for fixed wireless access, and to the new IEEE 802.16e standard with mobility support [7], [3]. Table 2 lists its characteristics.
SAP
Table 2. WiMax characteristics [3]
MAC
Parameters Maximum Data rate Frequency Band Modulation / Coding
802.16 32-134 Mbps
802.16a
802.16e
75Mbps
15 Mbps
10-66 GHz
2-11 GHz
2-6 GHz
QPSK /16QAM /64 QAM
OFDM QPSK/ 16QAM /64 QAM
OFDM QPSK/ 16QAM /64 QAM
As mentioned above the physical layer characteristics such as modulation/coding, access methods and frequency bands are different among the three kinds of the above systems.
3. Suggested integration model There are several ways of interconnecting networks. When two or more networks are interconnected at the MAC or data link layer, the type of the device is called bridge. When two or more networks are interconnected at the network layer, the type of the device is called router. We know MAC sub-layer deals with the problems of the coordinating the users access to the shared physical medium and each MAC standard is associated to a specific physical layer [8]. Main functions of MAC are (Fig. 1): - Mapping between logical channels and transport channels; - Selection of appropriate Transport Format (TF) for each Transport Channel depending on the instantaneous source rate; - Priority handling between data flows of one UE; - Priority handling between UEs by means of the dynamic scheduling;
Logical Link Control (LLC) Logical Channel
Medium Access Control (MAC) Transport Channel
SAP
Physical Layer
Fig. 1 Layered structure According to the above MAC characteristics we may redesign a suitable software layout to handle all the above functions for the tree kinds of the above systems (see Fig.2)
MAC 3GPP TS 25.321
MAC IEEE 802.11
MAC IEEE 802.16
MAC IEEE 802.3
Fig. 2 New adaptive MAC Layout (AMAC) should support three different MAC protocols Since the above systems may be connected to the wired internet network, we added IEEE 802.3 in the proposed layout. According to the generic MAC layout resulting from MAC functions, this new adaptive MAC sub-layer (AMAC) should include the following units: Multiplexer/De-multiplexer units, Scheduling/ Priority handler unit, TF selector, segmentation/ reassembly units and some other units. Therefore we found out the Fig. 3 which will be included in the new defined module Base Station Bridge (BSB). The suggested Base Station Bridge (BSB) will include the new layout as in Fig. 2. This is a bridge because it may transfer the information from AMAC to
Ethernet. This information from the Ethernet then is conveyed to IP core. Base Station Bridge (BSB) should also support functions such as channel assignment, H.O., power control, in addition to layer two processing. Besides, it should support transmit/receive data with the hierarchical rates (STM, E1, E3, …) and transfer data to IP core. In this configuration SGSN and GGSN of the traditional system may adhere to each other and move to BSB (Fig.4). Besides, in this configuration voice is converted to VoIP and all nodes may be interpreted as TCP/IP nodes.
[2] D. Niyato, E. Hossain, “Integration in WiMax and WiFi: Optimal Pricing for Bandwidth Sharing”, IEEE Communications Magazine, Pages 140-146, May 2007. [3] C. Smith, 3G Wireless with WiMax and Wi-Fi: 802.16 and 802.11, McGraw-Hill, 2005. [4] M. Lundan, I. Curcio, “Mobile Streaming Services in WCDMA networks”, 10th IEEE Symposium on Computers and Communications (ISCC 2005). [5] H. Holma, A. Toskala, WCDMA for UMTS, John Wilely & Sons, 4th edition, 2007. [6] A. Prasad, 802.11 WLANs and IP Networking: Security, QoS, Mobility, Artech House, 2005. [7] B. Li, Y. Kin, C. Ping, C. L. Gwee, “A Survey on Mobile WiMax”, IEEE Communications Magazine, Pages 70-75, Dec. 2007.
LLC
MAC IEEE 802.3
AMAC
[8] A. Leon Garical, L, Widjaja, Networks: Fundamental Concepts and Key Architectures, Mac Graw Hill, 2004.
SAP
UMTS Node B
UMTS Physical Layer 3GPP TS 25.301 & TS 25.312
WLAN Physical Layer IEEE 802.11
WiMax Physical Layer IEEE 802.16
SDH / PDH
MS
TDM / Ethernet
WLAN AP
4. Conclusion Wireless telecommunication systems convergence is not avoidable. We can reduce network cost, improve QoS and integrate real time and non-real time services using the integrated networks via IP backbone. By the suggested Base Station Bridge we can reduce the network hardware and reach to the unified backbone and services and therefore reduce the network cost.
Base Station Bridge
Ethernet
Fig. 3 New layout MS
WiMax Ethernet BTS
STM
MS IP core
5. References [1] J. Hu, W. W. Lu, “Open Wireless Architecture-The Core to 4G Mobile Communications”, International Conference on Communication Technology, ICCT, 2003.
Fig. 4 Mixed configuration of three kinds of wireless systems
