一鼓作气,再而衰,三而歇 - 分析9

策略决定企业的成败。

P1这一轮的攻势受到多人的欣赏和谈论。
但我认为如果以战略方针来看，
P1这一系列的策略不但无法为公司带来优势，
也使其一步一步走向毁灭性的道路。

我有三条理由。

第一条:
Michael Lai对其铺天盖地的策略的解释为：包装。
的确，我们看到包装的执行可以说很成功。
那么，我们就该问:为何包装？

包装是导火线，是用来导向市场的占有量。
但这一次P1的包装策略，却无法一次性的拿下市场。
纯粹只是包装，
热潮一过，一切回到包装之前的情况。

孙子说:一鼓作气,再而衰,三而歇.

为何无法一鼓作气拿下市场？
我认为原因很简单，就这么一条：
这一次的铺天盖地的宣传，是在没有创造胜利的条件下进行。
导火线烧到尾，没有接应到火药。
也就是说,产品不到位.
换成孙子兵法的说法，
这是在不具备战胜敌人的条件下仓促出战。
Pre-condition没有准备好。
没有胜利的条件，怎样有胜利的结果？

结果，其财力元气大伤，
需要一段时间来恢复元气。

第二条：
宣传的路线有侵略性、攻击性。
而侵略对象竟然是这一区域的霸主。
虽然TM的确每况愈下，
但这一举会直接引发TM的仇意和敌意，
激发敌人对你的战斗力。
兵家之忌啊！
因为你在帮助你的敌人提高战斗力和警觉性。

再来一条，
在自己实力还未强大之前就先去挑拨敌人，
完全违反了孙子的基本法：
故用兵之法，十则围之，五则功之，倍则分之，少则能守之。
这是完全没有根据敌我之间的差异而量身定作策略，
是个抱着侥幸的成份的进攻，
是个险棋。

第三条：
在自己还没站稳脚步，就急于占领更多地方。
东马、新加玻等等，
只要有机会，就去争取扩张。
这样一来，
兵力、资源、集中力都被分散了。
以一击十，
又再犯了兵忌。

看起来，你在扩张自己的市场，
实际上，你是在削弱自己和不同敌人的对比实力。
更何况你是没有根基地，
会有全盘落空的可能性。

没有创造胜利的条件下大军进攻、选择敌人的对象失误、没有量身定作的策略、占有地还没稳定就到处讨伐，
一条一条的致命策略，
一步一步的风险抵押。。。
如果P1的决策人还没看清楚这些掌握点，
很快的，它将陷入困境。

主动权 - 分析8

何谓主动权?
主动权有多重要?

胜利是需要计划的成功执行.
而计划的执行需要拥有主动权,
因为被动是无法执行想要的想法和计划.

而在合作的形式或是对敌的局面,
牵涉的个体都归类于主动和被动.
当然,没有一方希望处于被动,
这就造成了一种局面: 主动和被动的交替.

要怎样从被动变主动?
需要有条件.
条件可以是财势,军事,政治,外交,
甚至历史背景.
还有一个条件是可以被创造的:
创新.

纵观宽频和语音市场,
缺乏一个杀手铜: application.
这可以是任何形式的附加服务.
也可以是地理方式(graphically)的提供资讯.
只要拥有这类型的独特杀手铜,
就可以一次性地拿下整个市场.

兵马未动,粮草先行.

兵马未动,粮草先行.
在带兵打仗之前,粮草必须先准备和运行.

古人的粮草,就如我们现代人的生意资本.
资本先筹集,事情就容易得多了.

当资本不够别家雄厚但又不得不打这场仗的时候,
就必须出奇招.
比方说,
先声夺人,抢在人家之前先拔头筹.
又比如说,
虚张声势,
就如曹操在赤壁之战前宣称80万兵,实质上只有30万.

但是,虚里必须带实.
这样才能实实虚虚,以假带真.
在制造虚像的同时,必须捉紧时机巩固真实能力.
总不能从头到尾只在呈现虚像.

把太多精力花费在制造虚像,
就失去金钱和时间来加强实力.
把太多资金耗尽在宣传上,
就失去金钱和时间来加强产品实力.

不是说不必宣传,
这里强调的是适量,
不是过量.
过量的确能制造铺天盖地的感觉,
但之后虚弱必然浮现于地面,
而且如果拿捏错误必然元气大伤.

那么,对手一反击,
是否兵败如山?

Brief introduction of OFDM

OFDM has been the accepted standard for digital TV broadcasting. European DAB and DVB-T standards use OFDM. HIPERLAN 2 standard is also using OFDM techniques and so is the 5 GHz extension of IEEE 802.11 standard. ADSL and VDSL use OFDM. More recently, IEEE 802.16 has standardized OFDM for both Fixed and Mobile WiMAX.

In communication channels, frequency selective fading occurs when channel introduces time dispersion and the delay spread is larger than the symbol duration. The delay spread is the time spread between the arrival of the first and last multipath signal received at the receiving end. As a result, it will lead to intersymbol interference (ISI), where a received symbol can be influenced by previous symbol. With high data rate, the symbol duration can be very small. Therefore, the number of symbols that are affected by ISI can be large. In general, when the delay spread is less than the symbol length, the channel is flat fading. On the other hand, when the delay spread is much larger than the symbol length, the channel is frequency selective fading.

In fact, frequency selective fading is difficult to be compensated because the fading charateristics is random and not predictable due to the ever-changing environments. Due to this reason, multicarrer modulation (MCM) techniques such as orthogonal frequency division multiplexing (OFDM) and discrete multitone (DMT) modulation have become popular for high-speed wireline and wireless communication systems due to its robustness against frequency selective channels. The concept of MCM is to partition a broadband channel into a large number of narrowband subcahnnels, thus converting a frequency-selective channel into a collection of frequency-flat channels. In other words, we generate closely-spaced orthogonal subcarriers which are used to carry data, where the data is divided into several parallel data streams or channels, one for each subcarriers. Each subcarrier is modulated with a conventional modulation scheme, such as quadrature amplitude modulation (QAM), at a low symbol rate, thus maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.

As such, the transmission can achieve a high data rate while maintaining long symbol duration which reduces the effects of ISI. Reducing the effects of ISI yields a simple equalization. The equalization is performed in each subchannel by scaling back the received signal by an appropriate factor. Therefore, we can have a simple receiver structure. The implementations of MCM make use of an inverse fast Fourier transform (IFFT) for the modulation and a fast Fourier transform (FFT) for the demodulation to create orthogonal subchannels. After the information bits are grouped, coded and modulated, they are segmented by the serial-to-parallel converter before being fed into N-point IFFT to obtain the time domain OFDM symbols.

At the receiver, after passing through the analog-to-digital (A/D) and removing CP, the signals are converted from serial to parallel. Then N-point FFT is used to transform the data back to frequency domain. Finally, the information bits are obtained through the channel equalization and demodulation process.

(From my thesis introduction.)

What is MIMO?

Multiple-input and multiple-output (MIMO), is the use of multiple antennas at both the transmitter and receiver to improve communication performance. It is one of several forms of smart antenna technology. MIMO technology has attracted attention in wireless communications due to the significant increases in data throughput and link range without additional bandwidth or transmit power. It achieves this by higher spectral efficiency (more bits per second per hertz of bandwidth) and link reliability or diversity (reduced fading).

3 main categories: precoding, spatial multiplexing and diversity coding.

1. Precoding is multi-layer beanforming in a narrow sense or all spatial processing at the transmitter in a wide-sense. In (single-layer) beamforming, the same signal is emitted from each of the transmit antennas with appropriate phase (and sometimes gain) weighting such that the signal power is maximized at the receiver input. The benefits of beamforming are to increase the signal gain from constructive combining and to reduce the multipath fading effect. In the absence of scattering, beamforming results in a well defined directional pattern, but in typical cellular conventional beams are not a good analogy. When the receiver has multiple antennas, the transmit beamforming cannot simultaneously maximize the signal level at all of the receive antenna and precoding is used. Note that precoding requires knowledge of the channel state information (CSI) at the transmitter.

2. Spatial multiplexing requires MIMO antenna configuration. In spatial multiplexing, a high rate signal is split into multiple lower rate streams and each stream is transmitted from a different transmit antenna in the same frequency channel. If these signals arrive at the receiver antenna array with sufficiently different spatial signatures, the receiver can separate these streams, creating parallel channels for free. Spatial multiplexing is a very powerful technique for increasing channel capacity at higher Signal to Noise Ratio (SNR). The maximum number of spatial streams is limited by the lesser in the number of antennas at the transmitter or receiver. Spatial multiplexing can be used with or without transmit channel knowledge.

3. Diversity Coding techniques are used when there is no channel knowledge at the transmitter. In diversity methods a single stream (unlike multiple streams in spatial multiplexing) is transmitted, but the signal is coded using techniques called space-time coding (STC). The signal is emitted from each of the transmit antennas using certain principles of full or near orthogonal coding. Diversity exploits the independent fading in the multiple antenna links to enhance signal diversity. Because there is no channel knowledge, there is no beamforming or array gain from diversity coding.

(Modified from wikipedia.)

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.)