政府宏观调控的三种组合

宏观调控的时机和力度很重要,而且要有节奏地多次小步微调.

1. 手段组合

(a) 经济手段
(b) 法律手段
(c) 行政手段

2. 政策组合

(a) 货币信贷政策
(b) 财政税收政策
(c) 土地政策
(d) 产业政策
(e) 外汇政策


3. 工具组合

(a) 利率
(b) 存款准备金率

(Quoted from Sinchew)

政府宏观控制市场

1. 稳定物价水平
2. 稳定增长
3. 充分就业
4. 平衡国际收支
5. 资本市场稳定
6. 促进发展
7. 协调平等

Performance studies of time-domain equalizers over medium-voltage power-line communications

Power-line communication (PLC) technology uses the existing power cable infrastructure for communication purposes [1]. This technology does not involve any installation costs due to the readily availability of power-line grids. The electric power lines are classified into the high (larger than 100 kV), medium (1-100 kV) and low (smaller than 1 kV) voltage networks. High-voltage lines are usually not used for data transmission due to the excessive noise. Medium-voltage lines are routed from the substations to the neighborhood transformers, and can be used to form the backbone of data over power-line infrastructure. Low-voltage lines are routed from the neighborhood transformers to homes.

Orthogonal frequency division multiplexing (OFDM) modulation has been proposed as the modulation scheme for PLC networks due to its many desirable features [1]. However, if the length of the channel impulse response L is longer than that of the cyclic prefix (CP), inter-symbol interference (ISI) will arise. One of the possible solutions to combat ISI in PLC networks is to use a channel shortener, which is commonly known as time-domain equalizer (TEQ), at the receiving end to shorten the channel. A number of the TEQ methods [2-4] have been proposed for digital subscriber loop (DSL) systems. However, no thorough study on the implementation of TEQs over medium-voltage power-line communication (MV-PLC) networks has been reported yet. This under-reported area urges a motivation to investigate the potential performance improvements with a TEQ incorporated in MV-PLC networks. Different from the DSL channels, the increase of the number of branches along the transmission path increases the L [5], thus giving rise to strong ISI in the MV-PLC channels. In addition, the MV-PLC channels are worsen and afflicted with colored background noise, narrowband interference and impulsive noise, and thus exhibit remarkable differences from the DSL channels. Therefore, the aim of our study is to make the performance assessments on three major TEQ methods in such a hostile medium, and to provide the insights on the deployment of TEQs in MV-PLC networks.

1. S. Galli and O. Logvinov, “Recent developments in the standardization of power line communications within the IEEE,” IEEE Communications Magazine, vol. 46, no. 7, pp. 64-71, July, 2008.
2. N. Al-Dhahir and J. M. Cioffi, “Efficiently computed reduced-parameter input-aided MMSE equalizers for ML detection: A unified approach,” IEEE Trans. Inform. Theory, vol. 42, pp. 903-915, May, 1996.
3. P. J. W. Melsa, R. C. Younce, and C. E. Rohrs, “Impulse response shortening for discrete multitone transceivers,” IEEE Trans. Commun., vol. 44, pp.1662-1672, December, 1996.
4. G. Arslan, B. L. Evans, and S. Kiaei, “Equalization for discrete multitone receivers to maximize bit rate,” IEEE Trans. Signal Processing, vol. 49, pp. 3123-3135, December, 2001.5. J. Anatory, 5. N. Theethayi, M. M. Kissaka, N. H. Mvungi, and R. Thottappillil, “The effects of load impedance, line length, and branches in the BPLC-transmission-lines analysis for medium-voltage channel,” IEEE Transactions on Power Delivery, vol. 22, no. 4, pp. 2156-2162, October, 2007.

(From my paper.)

Time-domain equalizer

Multicarrier modulation has been employed in wireline and wireless communication systems due to its robustness against frequency selective channels [1], [2]. The implementation of multicarrier modulation, such as orthogonal frequency division multiplexing (OFDM) and discrete multitone (DMT), utilizes the inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) algorithm to create orthogonal subchannels.

However, a spectrally shaped channel destroys the orthogonality between subchannels, giving rise to inter-carrier interference (ICI) as well as inter-symbol interference (ISI) which degrades the system performance. One way to prevent ICI/ISI is to append a cyclic prefix (CP) to each symbol block. In particular, ISI is eliminated when Nb ≥ L – 1 where Nb and L denote the length of the CP and channel impulse response, respectively. For channels where Nb < L – 1, a channel shortener, commonly known as a time-domain equalizer (TEQ) [3], [4], [5], [6], [7] can be placed at the receiving end to shorten the channel. Therefore, a TEQ is useful for mitigating ISI and improving system performance.

References
[1] J. A. C. Bingham, “Multicarrier modulation for data transmission: An idea whose time has come,” IEEE Commun. Mag., vol. 28, no. 5, pp. 5-14, May 1990.
[2] Z. Wang and G.B. Giannakis, “Wireless multicarrier communications,” IEEE Signal Processing Mag., vol. 17, pp. 29–48, May 2000.
[3] N. Al-Dhahir and J. M. Cioffi, “Efficiently computed reduced-parameter input-aided MMSE equalizers for ML detection: A unified approach,” IEEE Trans. Inform. Theory, vol. 42, pp. 903-915, May 1996.
[4] P. J. W. Melsa, R. C. Younce, and C. E. Rohrs, “Impulse response shortening for discrete multitone transceivers,” IEEE Trans. Commun., vol. 44, pp.1662-1672, Dec. 1996.
[5] G. Arslan, B. L. Evans, and S. Kiaei, “Equalization for discrete multitone receivers to maximize bit rate,” IEEE Trans. Signal Processing, vol. 49, pp. 3123-3135, Dec. 2001.
[6] B. Farhang-Boroujeny and M. Ding, “Design methods for time-domain equalizer in DMT transceivers,” IEEE Trans. Communications, vol. 49, no. 3, pp. 554–562, 2001.R. K. Martin, J. Balakrishnan,W. A. Sethares, and C. R. Johnson Jr., “A blind, adaptive TEQ for multicarrier systems,” IEEE Signal Processing Letters, vol. 9, no. 11, pp. 341-343, 2002.
[7] R. K. Martin, J. Balakrishnan,W. A. Sethares, and C. R. Johnson Jr., “A blind, adaptive TEQ for multicarrier systems,” IEEE Signal Processing Letters, vol. 9, no. 11, pp. 341-343, 2002.


(From my paper.)

Wimax Network Architecture

The network reference model envisions a unified network architecture for supporting fixed, nomadic, and mobile deployments and is based on an IP service model. The overall network architecture may be divided into three parts:

• Mobile Stations (MS) used by the end user to access the network.
• The access service network (ASN), which comprises one or more base stations and one or more ASN gateways that form the radio access network at the edge.
• Connectivity service network (CSN), which provides IP connectivity and all the IP core network functions.

The functions:

1. Base station (BS): The BS is responsible for providing the air interface to the MS. Additional functions that may be part of the BS are micromobility management functions, such as handoff triggering and tunnel establishment, radio resource management, QoS policy enforcement, traffic classification, DHCP (Dynamic Host Control Protocol) proxy, key management, session management, and multicast group management.
2. Access service network gateway (ASN-GW): The ASN gateway typically acts as a layer 2 traffic aggregation point within an ASN. Additional functions that may be part of the ASN gateway include intra-ASN location management and paging, radio resource management and admission control, caching of subscriber profiles and encryption keys, AAA client functionality, establishment and management of mobility tunnel with base stations, QoS and policy enforcement, foreign agent functionality for mobile IP, and routing to the selected CSN.
3. Connectivity service network (CSN): The CSN provides connectivity to the Internet, ASP, other public networks, and corporate networks. The CSN is owned by the NSP and includes AAA servers that support authentication for the devices, users, and specific services. The CSN also provides per user policy management of QoS and security. The CSN is also responsible for IP address management, support for roaming between different NSPs, location management between ASNs, and mobility and roaming between ASNs.

(Modified from wikipedia.)