Niranjan Balasubramanian

Energy consumption in mobile phones: a measurement study and implications for network applications

In this paper, we present a measurement study of the energy consumption characteristics of three widespread mobile networking technologies: 3G, GSM, and WiFi. We find that 3G and GSM incur a high tail energy overhead because of lingering in high power states after completing a transfer. Based on these measurements, we develop a model for the energy consumed by network activity for each technology.n Using this model, we develop TailEnder, a protocol that reduces energy consumption of common mobile applications. For applications that can tolerate a small delay such as e-mail, TailEnder schedules transfers so as to minimize the cumulative energy consumed meeting user-specified deadlines. We show that the TailEnder scheduling algorithm is within a factor 2x of the optimal and show that any online algorithm can at best be within a factor 1.62x of the optimal. For applications like web search that can benefit from prefetching, TailEnder aggressively prefetches several times more data and improves user-specified response times while consuming less energy. We evaluate the benefits of TailEnder for three different case study applications - email, news feeds, and web search - based on real user logs and show significant reduction in energy consumption in each case. Experiments conducted on the mobile phone show that TailEnder can download 60% more news feed updates and download search results for more than 50% of web queries, compared to using the default policy.

Exploring reductions for long web queries

Long queries form a difficult, but increasingly important segment for web search engines. Query reduction, a technique for dropping unnecessary query terms from long queries, improves performance of ad-hoc retrieval on TREC collections. Also, it has great potential for improving long web queries (upto 25% improvement in NDCG@5). However, query reduction on the web is hampered by the lack of accurate query performance predictors and the constraints imposed by search engine architectures and ranking algorithms.n In this paper, we present query reduction techniques for long web queries that leverage effective and efficient query performance predictors. We propose three learning formulations that combine these predictors to perform automatic query reduction. These formulations enable trading of average improvements for the number of queries impacted, and enable easy integration into the search engines architecture for rank-time query reduction. Experiments on a large collection of long queries issued to a commercial search engine show that the proposed techniques significantly outperform baselines, with more than 12% improvement in NDCG@5 in the impacted set of queries. Extension to the formulations such as result interleaving further improves results. We find that the proposed techniques deliver consistent retrieval gains where it matters most: poorly performing long web queries.

A comparison of sentence retrieval techniques

Identifying redundant information in sentences is useful for several applications such as summarization, document provenance, detecting text reuse and novelty detection. The task of identifying redundant information in sentences is defined as follows: Given a query sentence the task is to retrieve sentences from a given collection that express all or some subset of the information present in the query sentence. Sentence retrieval techniques rank sentences based on some measure of their similarity to a query. The effectiveness of such techniques depends on the similarity measure used to rank sentences. An effective retrieval model should be able to handle low word overlap between query and candidate sentences and go beyond just word overlap. Simple language modeling techniques like query likelihood retrieval have outperformed TF-IDF and word overlap based methods for ranking sentences. In this paper, we compare the performance of sentence retrieval using different language modeling techniques for the problem of identifying redundant information.

Predicting query performance on the web

Predicting the performance of web queries is useful for several applications such as automatic query reformulation and automatic spell correction. In the web environment, accurate performance prediction is challenging because measures such as clarity that work well on homogeneous TREC-like collections, are not as effective and are often expensive to compute. We present Rank-time Performance Prediction (RAPP), an effective and efficient approach for online performance prediction on the web. RAPP uses retrieval scores, and aggregates of the rank-time features used by the document- ranking algorithm to train regressors for query performance prediction. On a set of over 12,000 queries sampled from the query logs of a major search engine, RAPP achieves a linear correlation of 0.78 with DCG@5, and 0.52 with NDCG@5. Analysis of prediction accuracy shows that hard queries are easier to identify while easy queries are harder to identify.

Learning to select rankers

Combining evidence from multiple retrieval models has been widely studied in the context of of distributed search, metasearch and rank fusion. Much of the prior work has focused on combining retrieval scores (or the rankings) assigned by different retrieval models or ranking algorithms. In this work, we focus on the problem of choosing between retrieval models using performance estimation. We propose modeling the differences in retrieval performance directly by using rank-time features - features that are available to the ranking algorithms - and the retrieval scores assigned by the ranking algorithms. Our experimental results show that when choosing between two rankers, our approach yields significant improvements over the best individual ranker.

Automatic generation of topic pages using query-based aspect models

We investigate the automatic generation of topic pages as an alternative to the current Web search paradigm. We describe a general framework, which combines query log analysis to build aspect models, sentence selection methods for identifying relevant and non-redundant Web sentences, and a technique for sentence ordering. We evaluate our approach on biographical topics both automatically and manually, by using Wikipedia as reference.

Syntactic Query Models for Restatement Retrieval

We consider the problem of retrieving sentence level restatements. Formally, we define restatements as sentences that contain all or some subset of information present in a query sentence. Identifying restatements is useful for several applications such as multi-document summarization, document provenance, text reuse and novelty detection. Spurious partial matches and term dependence become important issues for restatement retrieval in these settings. To address these issues, we focus on query models that capture relative term importance and sequential term dependence. In this paper, we build query models using syntactic information such as subject-verb-objects and phrases. Our experimental results on two different collections show that syntactic query models are consistently more effective than purely statistical alternatives.

BEYOND RANKED LISTS IN WEB SEARCH: AGGREGATING WEB CONTENT INTO TOPIC PAGES

We investigate the automatic generation of topic pages as an alternative to the current Web search paradigm. Topic pages explicitly aggregate information across documents, filter redundancy, and promote diversity of topical aspects. We propose a novel framework for building rich topical aspect models and selecting diverse information from the Web. In particular, we use Web search logs to build aspect models with various degrees of specificity, and then employ these aspect models as input to a sentence selection method that identifies relevant and non-redundant sentences from the Web. Automatic and manual evaluations on biographical topics show that topic pages built by our system compare favorably to regular Web search results and to MDS-style summaries of the Web results on all metrics employed.