Crosstalk Measurements in DSL Rings Khaled Ali and Geoffrey Messier Dept. of Electrical & Computer Eng., University of Calgary, Calgary, Alberta, Canada Stephen Cooke Genesis Technical Systems, Calgary, Alberta, Canada Abstract—Due to the inverse relation between cable length and transmission bit rate, many current DSL deployments do not truly benefit from the wide spectrum of VDSL2. In this paper, we propose a new DSL network technology, called DSL Rings (DSLRs), to overcome the challenge of long cable runs in DSL networks. Utilizing MIMO techniques from the central office to the pedestal and a ring network between the pedestal and the houses, DSLR achieves aggregate transmission rates up to 225 Mbits/s. Measurements on Cat3 cables are conducted to characterize crosstalk interference that is unique to this new architecture. The achievable symbol bit rates are then calculated using these measurements. The results demonstrate the effectiveness of the proposed architecture in providing VDSL2 technology over fiber to the exchange (FTTEx) deployments. I. I NTRODUCTION Digital Subscriber Line (DSL) technology allows data trans- mission over public service telephone networks (PSTNs). A PSTN utilizes twisted-pairs of copper wires as a medium for transmitting speech signals. Since human speech is in the range of 300 Hz to 3400 Hz, higher frequencies can be used for transmitting data over existing PSTNs [1]. The very high bit rate digital subscriber line 2 (VDSL2) technology offers the highest data rates achieved over copper twisted-pairs. However, these high data rates are only avail- able over short distances. VDSL2 uses a wider bandwidth (from 25 kHz up to 30 MHz) and has a longer reach than VDSL. The VDSL2 international telecommunication union- telecommunication standardization sector (ITU-T) standard, G.993.2 [2], specifies four major band plans, with eight profiles, where each of these band plans is suitable for a specific hybrid fiber twisted pair (HFTP) deployment [3]. Band plan 8 (4 profiles: 8a, 8b, 8c, and 8d) utilizes a bandwidth of 8.6 MHz with data rates up to 50 Mb/s. Band plan 12 (2 profiles: 12a and 12b) utilize a bandwidth of 12 MHz and has a maximum data rate of 68 Mb/s. Both band plan 8 and 12 are suitable for fiber to the exchange (FTTEx) deployments, with an 8 kft maximum length of twisted-pair run. Band plan 17 (1 profile: 17a) utilizes a bandwidth of 17.7 MHz and provides a maximum data rate of 100 Mb/s. This band plan is suitable fiber to the cabinet (FTTCab) deployments, where the maximum length of the twisted-pairs is approximately 5 kft. Finally, the Band plan 30 (1 profile: 30a) utilizes the entire VDSL2 bandwidth and offer data rates up to 200 Mb/s. This band plan is suitable for HFTP deployments where the twisted-pair length does not exceed 1 kft, such as fiber to the building (FTTB) deployments. A major drawback of DSL is the inverse relation between the length of the cable used and the data transmission rate that can be achieved. For instance, the transmission rate drops from above 100 Mbits/s to less than 30 Mbits/s after the first 500 m of a very high bit rate digital subscriber line 2 (VDSL2) system [3]. The contribution of this paper is to propose a new network architecture, called DSL Rings (DSLRs), capable of achieving aggregate bit rates of up to 225 Mbit/s. A key feature of this network is the installation of an active device, called a convergence node (CN), into the pedestal. Capable of being powered using the twisted-pairs entering the pedestal, the CN increases data rate in two ways. First, throughput from the pedestal to the central office is increased through the use of multiple-input multiple-output (MIMO) bonding techniques. Second, throughput from the pedestal to the home is increased using a new ring network architecture. This ring reduces cable run lengths and, as a result, comes closer to realizing the full potential of VDSL2 over an FTTEx deployment. Noise in DSL can be classified as intrinsic, such as thermal noise and crosstalk, or extrinsic, such as impulsive noise and radio frequency interference. Extrinsic noise is intermittent in nature and its power levels are varying. On the other hand, intrinsic noise power levels are usually slowly changing, and thus, its power levels can be estimated by the transceivers [4]. Crosstalk (xTalk), which occurs when a signal power leaks from one twisted-pair to another, is the main cause of errors in a DSL network [5]. There are two types of crosstalk: near end crosstalk (NEXT) and far end cross talk (FEXT). NEXT occurs among twisted-pairs when an interfering signal is transmitted from the same end of the cable as the receiver, while FEXT occurs when an interfering signal is transmitted from the end of the cable that is opposite to the receiver [6]. DSLR replaces the low rate dedicated links to each house with a shared high rate link. One drawback of this network is that it suffers from considerable near end crosstalk (NEXT). A second contribution of this paper is to conduct ring network crosstalk measurements on real telephone cables. These mea- surements are used to demonstrate that this NEXT does not prevent the proposed architecture from achieving very high throughput. The rest of this paper is organized as follows. In Section II, the proposed DSLR network model is discussed; after which, in Section III, measurements that study the xTalk environment in DSLR networks are presented. Analysis of the achievable bit rate in a DSLR network is presented in Section IV. Finally,